presubmit: upload findings only if resultdb is enabled

Code findings will be uploaded to resultdb. If resultdb is not
enabled, exception will be thrown.

Bug: 404837554
Change-Id: I76ff82d6ecdd987fe08fdd703b67a1171d85eed0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6479007
Commit-Queue: Gavin Mak <gavinmak@google.com>
Auto-Submit: Yiwei Zhang <yiwzhang@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

recipes/recipe_modules/presubmit/api.py

@@ -214,7 +214,7 @@ class PresubmitApi(recipe_api.RecipeApi):
           ' while running presubmit checks.'
           ' Please [file a bug](https://issues.chromium.org'
           '/issues/new?component=1456211)')
-    if step_json:
+    if step_json and self.m.resultdb.enabled:
       self._upload_findings_from_result(step_json)
     return raw_result