Factor out some common Complement CI setup commands to a script. (#13157)

.github/workflows/tests.yml

@@ -332,34 +332,13 @@ jobs:
             database: Postgres
 
     steps:
-      # The path is set via a file given by $GITHUB_PATH. We need both Go 1.17 and GOPATH on the path to run Complement.
-      # See https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#adding-a-system-path
-      - name: "Set Go Version"
-        run: |
-          # Add Go 1.17 to the PATH: see https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-Readme.md#environment-variables-2
-          echo "$GOROOT_1_17_X64/bin" >> $GITHUB_PATH
-          # Add the Go path to the PATH: We need this so we can call gotestfmt
-          echo "~/go/bin" >> $GITHUB_PATH
-
-      - name: "Install Complement Dependencies"
-        run: |
-          sudo apt-get -qq update && sudo apt-get install -qqy libolm3 libolm-dev
-          go get -v github.com/haveyoudebuggedit/gotestfmt/v2/cmd/gotestfmt@latest
-
       - name: Run actions/checkout@v2 for synapse
         uses: actions/checkout@v2
         with:
           path: synapse
 
-      - name: "Install custom gotestfmt template"
-        run: |
-          mkdir .gotestfmt/github -p
-          cp synapse/.ci/complement_package.gotpl .gotestfmt/github/package.gotpl
-
-      # Attempt to check out the same branch of Complement as the PR. If it
-      # doesn't exist, fallback to HEAD.
-      - name: Checkout complement
-        run: synapse/.ci/scripts/checkout_complement.sh
+      - name: Prepare Complement's Prerequisites
+        run: synapse/.ci/scripts/setup_complement_prerequisites.sh
 
       - run: |
           set -o pipefail