.github: re-pin github-script to v3

When tsscr bumped the version of the action to v6, we experienced some
failures in our nightly runs.

To make the action operable again, we pin the action to the former: v3.

Author: lbajolet-hashicorp

.github/workflows/nightly-release.yml

@@ -38,7 +38,7 @@ jobs:
           echo "BUILD_OUTPUT_LIST=$(cat tmp2.txt | tr '\n' ',' | perl -ple 'chop')" >> $GITHUB_ENV
           rm -rf tmp.txt && rm -rf tmp2.txt
       - name: Advance nightly tag
-        uses: actions/github-script@d7906e4ad0b1822421a7e6a35d5ca353c962f410 # v6.4.1
+        uses: actions/github-script@ffc2c79a5b2490bd33e0a41c1de74b877714d736 # v3
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           script: |