ci: use containers matrix name in github actions workflow (#789)

.github/workflows/using-action.yml

@@ -27,10 +27,14 @@ jobs:
       # https://github.com/cypress-io/github-action/issues/48
       fail-fast: false
       matrix:
-        # run 4 copies of the current job in parallel
-        # the actual items in the array do not matter
-        # we just need to "force" GitHub CI to create 4 jobs
-        machines: [1, 2, 3, 4]
+        # Run 4 copies of the current job in parallel.
+        # The name of the array (containers) and
+        # the actual items in the array (1, 2, 3, 4) do not matter.
+        # Based on the array, GitHub Actions will create
+        # 4 independently running parallel jobs
+        # (see https://docs.github.com/en/actions/using-jobs/using-a-matrix-for-your-jobs).
+        # Cypress Cloud load-balances the Cypress tests across the GitHub Actions jobs.
+        containers: [1, 2, 3, 4]
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -61,7 +65,7 @@ jobs:
         # run 2 copies of the current job in parallel
         # and they will load balance all specs
         os: ['ubuntu-22.04', 'windows-latest', 'macos-latest']
-        machines: [1, 2]
+        containers: [1, 2]
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout