ci: Update to check-spelling@v0.0.21

.github/actions/spelling/README.md

@@ -8,8 +8,10 @@ File | Purpose | Format | Info
 [excludes.txt](excludes.txt) | Files to ignore entirely | perl regular expression | [excludes](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-excludes)
 [only.txt](only.txt) | Only check matching files (applied after excludes) | perl regular expression | [only](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-only)
 [patterns.txt](patterns.txt) | Patterns to ignore from checked lines | perl regular expression (order matters, first match wins) | [patterns](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-patterns)
+[candidate.patterns](candidate.patterns) | Patterns that might be worth adding to [patterns.txt](patterns.txt) | perl regular expression with optional comment block introductions (all matches will be suggested) | [candidates](https://github.com/check-spelling/check-spelling/wiki/Feature:-Suggest-patterns)
+[line_forbidden.patterns](line_forbidden.patterns) | Patterns to flag in checked lines | perl regular expression (order matters, first match wins) | [patterns](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-patterns)
 [expect.txt](expect.txt) | Expected words that aren't in the dictionary | one word per line (sorted, alphabetically) | [expect](https://github.com/check-spelling/check-spelling/wiki/Configuration#expect)
-[advice.txt](advice.txt) | Supplement for GitHub comment when unrecognized words are found | GitHub Markdown | [advice](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-advice)
+[advice.md](advice.md) | Supplement for GitHub comment when unrecognized words are found | GitHub Markdown | [advice](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-advice)
 
-Note: you can replace any of these files with a directory by the same name (minus the `.txt` extension) and
-then include multiple files (with a `.txt` extension) inside that directory to merge multiple files together.
+Note: you can replace any of these files with a directory by the same name (minus the suffix)
+and then include multiple files inside that directory (with that suffix) to merge multiple files together.

.github/actions/spelling/advice.md

@@ -1,28 +1,25 @@
 <!-- See https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples%3A-advice --> <!-- markdownlint-disable MD033 MD041 -->
+<details><summary>If the flagged items are :exploding_head: false positives</summary>
 
-<details><summary>If you see a bunch of garbage</summary>
+If items relate to a ...
+* binary file (or some other file you wouldn't want to check at all).
 
-If it relates to a ...
-<details><summary>well-formed pattern</summary>
+  Please add a file path to the `excludes.txt` file matching the containing file.
 
-See if there's a [pattern](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples:-patterns) that would match it.
-
-If not, try writing one and adding it to the `patterns.txt` file.
+  File paths are Perl 5 Regular Expressions - you can [test](
+https://www.regexplanet.com/advanced/perl/) yours before committing to verify it will match your files.
 
-Patterns are Perl 5 Regular Expressions - you can [test](
-https://www.regexplanet.com/advanced/perl/) yours before committing to verify it will match your lines.
+  `^` refers to the file's path from the root of the repository, so `^README\.md$` would exclude [README.md](
+../tree/HEAD/README.md) (on whichever branch you're using).
 
-Note that patterns can't match multiline strings.
-</details>
-<details><summary>binary-ish string</summary>
+* well-formed pattern.
 
-Please add a file path to the `excludes.txt` file instead of just accepting the garbage.
+  If you can write a [pattern](https://github.com/check-spelling/check-spelling/wiki/Configuration-Examples:-patterns) that would match it,
+  try adding it to the `patterns.txt` file.
 
-File paths are Perl 5 Regular Expressions - you can [test](
-https://www.regexplanet.com/advanced/perl/) yours before committing to verify it will match your files.
+  Patterns are Perl 5 Regular Expressions - you can [test](
+https://www.regexplanet.com/advanced/perl/) yours before committing to verify it will match your lines.
 
-`^` refers to the file's path from the root of the repository, so `^README\.md$` would exclude [README.md](
-../tree/HEAD/README.md) (on whichever branch you're using).
-</details>
+  Note that patterns can't match multiline strings.
 
 </details>

.github/actions/spelling/allow.txt

@@ -0,0 +1,11 @@
+CODEOWNERS
+codeowners
+CORS
+cors
+github
+https
+ssh
+SUSE
+Suse
+ubuntu
+workarounds