test: add comprehensive unit tests for dependency_updater helper functions

- Add tests for generateGithubRepoUrl (valid + nil guard)
- Add tests for writeToVersionsJson (success + invalid path)
- Add tests for createVersionsEnv (basic, branch tracking, sorted output, invalid path)
- Add tests for writeToGithubOutput (normal + missing env var)
- Add tests for createCommitMessage in githubAction mode
- Add tests for updateVersionTagAndCommit (in-memory + file write)
- Add nil-safety guard to generateGithubRepoUrl for unknown keys

Increases test coverage from 0 to 389 lines across 12 test functions.

Author: Kewe63

dependency_updater/dependency_updater.go

@@ -407,5 +407,9 @@ func writeToGithubOutput(title string, description string, repoPath string) erro
 }
 
 func generateGithubRepoUrl(dependencies Dependencies, dependencyType string) string {
-	return "https://github.com/" + dependencies[dependencyType].Owner + "/" + dependencies[dependencyType].Repo
+	info := dependencies[dependencyType]
+	if info == nil {
+		return ""
+	}
+	return "https://github.com/" + info.Owner + "/" + info.Repo
 }