build: rename samples lint workflow to checkstyle to disambiguate branch protection with unit lint (#781)

Author: BenWhitehead

synthtool/gcp/templates/java_library/.github/workflows/samples.yaml

@@ -2,7 +2,7 @@ on:
   pull_request:
 name: samples
 jobs:
-  lint:
+  checkstyle:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2