fix: git cache (#38763)

1. always use "last commit cache"
2. correctly build the cache key for any input (SafeCacheKey)
3. fix the git note "last commit cache FIXME" and avoid OOM

modules/git/last_commit_cache_nogogit.go

@@ -11,9 +11,6 @@ import (
 
 // CacheCommit will cache the commit from the gitRepository
 func (c *Commit) CacheCommit(ctx context.Context, gitRepo *Repository) error {
-	if gitRepo.LastCommitCache == nil {
-		return nil
-	}
 	return c.recursiveCache(ctx, gitRepo, c.Tree(), "", 1)
 }