fix: disallow blame on directories (#6716)

- Don't allow the blame operation on directories.
- Added integration test.
- Resolves forgejo/forgejo#6533

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6716
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

routers/web/repo/blame.go

@@ -56,6 +56,11 @@ func RefBlame(ctx *context.Context) {
 		HandleGitError(ctx, "Repo.Commit.GetTreeEntryByPath", err)
 		return
 	}
+	if entry.IsDir() {
+		ctx.NotFound("Cannot blame directory", nil)
+		return
+	}
+
 	blob := entry.Blob()
 
 	ctx.Data["PageIsViewCode"] = true