Minor fixes for the yamllint CI. (#8302)

* Turn off a buggy check in the yamllint config.
* Drop yamllint flags. Reviewdog checks all changed files, and the line
  was misspelled anyway.

.github/workflows/reviewdog.yml

@@ -40,4 +40,3 @@ jobs:
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           reporter: github-pr-check
-          yamllintdd_flags: '.yamllint.yml .travis.yml .github/workflows/*.yml'

.yamllint.yml

@@ -26,5 +26,4 @@ rules:
   octal-values: enable
   quoted-strings: disable
   trailing-spaces: enable
-  truthy:
-    level: warning
+  truthy: disable