on `reup` update rev with latest tag if rev is a tag

[Araxeus]

imports:
    vscode: scripts/

git module vscode
    url: git://github.com/microsoft/vscode.git
    rev: 1.75.0

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peru reup -f

⏬

imports:
    vscode: scripts/

git module vscode
    url: git://github.com/microsoft/vscode.git
    rev: 1.75.1

Currently, the rev will be replaced with the latest commit hash instead of the latest tag
related to #193 (comment)

[Araxeus]

Implemented this myself in #234 since it seemed easy to do, and it shouldn't cause any breaking