TestTrackingCache_createTeardownInformers unit test is flakey

[erdii]

Discovered in: #504 (comment)

On #504 unit test failed in CI:

❌ TestTrackingCache_createTeardownInformers (10ms)
      trackingcache.go:307: TrackingCache: "level"=0 "msg"="waiting for new informer to sync" "gvk"="/v1, Kind=ConfigMap"
      trackingcache.go:310: TrackingCache: "level"=0 "msg"="informer synced successfully" "gvk"="/v1, Kind=ConfigMap"
      trackingcache.go:429: TrackingCache: "level"=0 "msg"="stopping informer" "gvk"="/v1, Kind=ConfigMap"
      trackingcache_test.go:117: FAIL:	Start(string)
          		at: [/home/runner/work/boxcutter/boxcutter/managedcache/trackingcache_test.go:74]
      trackingcache_test.go:117: FAIL: 3 out of 4 expectation(s) were met.
          	The code you are testing needs to make 1 more call(s).
          	at: [/home/runner/work/boxcutter/boxcutter/managedcache/trackingcache_test.go:117]

The test fails unreliably - most of the time it passes.
To reproduce I had to run the tests for managedcache in a loop:

# `-count 1` to sidestep go's test caching
while go test -test.fullpath=true -count 1 -timeout 30s pkg.package-operator.run/boxcutter/managedcache; do; done                                                 
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.007s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.009s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
ok      pkg.package-operator.run/boxcutter/managedcache 0.008s
--- FAIL: TestTrackingCache_createTeardownInformers (0.00s)
    /home/erdii/projects/redhat/github.com/package-operator/boxcutter/managedcache/trackingcache.go:307: TrackingCache: "level"=0 "msg"="waiting for new informer to sync" "gvk"="/v1, Kind=ConfigMap"
    /home/erdii/projects/redhat/github.com/package-operator/boxcutter/managedcache/trackingcache.go:310: TrackingCache: "level"=0 "msg"="informer synced successfully" "gvk"="/v1, Kind=ConfigMap"
    /home/erdii/projects/redhat/github.com/package-operator/boxcutter/managedcache/trackingcache.go:429: TrackingCache: "level"=0 "msg"="stopping informer" "gvk"="/v1, Kind=ConfigMap"
    /home/erdii/projects/redhat/github.com/package-operator/boxcutter/managedcache/trackingcache_test.go:117: FAIL:     Start(string)
                        at: [/home/erdii/projects/redhat/github.com/package-operator/boxcutter/managedcache/trackingcache_test.go:74]
    /home/erdii/projects/redhat/github.com/package-operator/boxcutter/managedcache/trackingcache_test.go:117: FAIL: 3 out of 4 expectation(s) were met.
                The code you are testing needs to make 1 more call(s).
                at: [/home/erdii/projects/redhat/github.com/package-operator/boxcutter/managedcache/trackingcache_test.go:117]
FAIL
FAIL    pkg.package-operator.run/boxcutter/managedcache 0.009s
FAIL

[erdii]

Found another one in https://github.com/package-operator/boxcutter/actions/runs/23859168311/job/69664200403#step:5:653

❌ TestTrackingCacheWatchErrorHandling_Get (20ms)
      trackingcache.go:307: TrackingCache: "level"=0 "msg"="waiting for new informer to sync" "gvk"="/v1, Kind=ConfigMap"
      trackingcache.go:120: TrackingCache: "level"=0 "msg"="error in reflector" "typeDescription"="" "err"="kaputt"
      trackingcache.go:429: TrackingCache: "level"=0 "msg"="stopping informer" "gvk"="/v1, Kind=ConfigMap"
      trackingcache_test.go:463: FAIL:	Start(string)
          		at: [/home/runner/work/boxcutter/boxcutter/managedcache/trackingcache_test.go:418]
      trackingcache_test.go:463: FAIL: 2 out of 3 expectation(s) were met.
          	The code you are testing needs to make 1 more call(s).
          	at: [/home/runner/work/boxcutter/boxcutter/managedcache/trackingcache_test.go:463]
      trackingcache.go:120: TrackingCache: "level"=0 "msg"="error in reflector" "typeDescription"="" "err"="kaputt"
      trackingcache.go:317: TrackingCache: "level"=0 "msg"="wait for informer sync canceled" "gvk"="/v1, Kind=ConfigMap"```