devops: properly trigger tests on internal test runners (#5453)

Author: aslushnikov

.github/workflows/trigger_tests.yml

@@ -15,8 +15,7 @@ jobs:
         curl -X POST \
           -H "Accept: application/vnd.github.v3+json" \
           -H "Authorization: token ${GH_TOKEN}" \
-          --data '{"event_type": "playwright_tests", "client_payload": {"foo": "${GH_REF}"}}' \
+          --data '{"event_type": "playwright_tests", "client_payload": {"foo": "${GITHUB_SHA}"}}' \
           https://api.github.com/repos/microsoft/playwright-internal/dispatches
       env:
         GH_TOKEN: ${{ secrets.REPOSITORY_DISPATCH_PERSONAL_ACCESS_TOKEN }}
-        GH_REF: ${{ github.ref }}