Pin actionlint docker image to sha256 digest (#42821)

* Pin actionlint docker image to sha256 digest

Agent-Logs-Url: https://github.com/Azure/azure-rest-api-specs/sessions/de091f51-8df0-4e27-9560-c21d7edec6e3

Co-authored-by: mikeharder <9459391+mikeharder@users.noreply.github.com>

* Apply suggestion from @mikeharder

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: mikeharder <9459391+mikeharder@users.noreply.github.com>
Co-authored-by: Mike Harder <mharder@microsoft.com>

Author: Copilot

.github/workflows/github-test.yaml

@@ -69,6 +69,6 @@ jobs:
 
       - if: ${{ matrix.folder == '.github' && matrix.os == 'ubuntu'}}
         name: Lint workflows
-        uses: docker://rhysd/actionlint:1.7.12
+        uses: docker://rhysd/actionlint:1.7.12@sha256:b1934ee5f1c509618f2508e6eb47ee0d3520686341fec936f3b79331f9315667
         with:
           args: -color -verbose