BOTMETA: label:docs (#36757)

Don't use different labels for docs, that's what is:pr and is:issue is
for.

Discussed and approved by dharmabumstead

Makes it easier to do label:docs label:networking to find all issues
and PRs

.github/BOTMETA.yml

@@ -1071,7 +1071,7 @@ files:
     keywords:
     - validate-modules
   docs/:
-    labels: docs_pull_request
+    labels: docs
     notify: dharmabumstead
   docs/docsite/rst/network/:
     labels: networking