chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/provider/protonvpn/updater/version.go

@@ -45,7 +45,7 @@ func getMostRecentStableTag(ctx context.Context, client *http.Client) (version s
 		}
 
 		if response.StatusCode != http.StatusOK {
-			return "", fmt.Errorf("%w: %s: %s", ErrHTTPStatusCodeNotOK, response.Status, data)
+			return "", fmt.Errorf("HTTP status code not OK: %s: %s", response.Status, data)
 		}
 
 		var tags []struct {