github: update workflow to use renamed branch

The presubmits were broken because it pointed to `master` which no
longer exists. It is now `main`. See https://github.com/google-github-actions/setup-gcloud

.github/workflows/linux.yml

@@ -52,12 +52,13 @@ jobs:
           PRIVATE_KEY: ${{ secrets.SSH_PRIVATE_KEY }}
           PUBLIC_KEY: ${{ secrets.SSH_PUBLIC_KEY }}
 
-      - name: Install Gcloud SDK
-        uses: google-github-actions/setup-gcloud@master
+      - name: Authenticate using ServiceAccount
+        uses: 'google-github-actions/auth@v2'
         with:
-          project_id: ${{ secrets.GCP_PROJECT_ID }}
-          service_account_key: ${{ secrets.GCP_SA_KEY }}
-          export_default_credentials: true
+          credentials_json: '${{ secrets.GCP_SA_KEY }}'
+
+      - name: Set up Cloud SDK
+        uses: 'google-github-actions/setup-gcloud@v2'
 
       - name: Deploy instance
         run: ../../.github/scripts/terraform-apply.sh ${{ matrix.distro }} ${{ matrix.agent_type }} ${{ matrix.version }}

.github/workflows/windows.yml

@@ -32,12 +32,13 @@ jobs:
           PRIVATE_KEY: ${{ secrets.SSH_PRIVATE_KEY }}
           PUBLIC_KEY: ${{ secrets.SSH_PUBLIC_KEY }}
 
-      - name: Install Gcloud SDK
-        uses: google-github-actions/setup-gcloud@master
+      - name: Authenticate using ServiceAccount
+        uses: 'google-github-actions/auth@v2'
         with:
-          project_id: ${{ secrets.GCP_PROJECT_ID }}
-          service_account_key: ${{ secrets.GCP_SA_KEY }}
-          export_default_credentials: true
+          credentials_json: '${{ secrets.GCP_SA_KEY }}'
+
+      - name: Set up Cloud SDK
+        uses: 'google-github-actions/setup-gcloud@v2'
 
       - name: Deploy instance
         run: ../../.github/scripts/terraform-apply.sh ${{ matrix.distro }} ${{ matrix.agent_type }} ${{ matrix.version }}