Use setup-go action

This was my first attempt to fix CI. Go 1.17 is no longer available on
runners (actions/runner-images#7276 maybe)
and I wondered if that might help with that.

Unfortunately I think not. But we should get some go build caching as a
side effect of using this action.

.github/workflows/ci.yaml

@@ -15,13 +15,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2 # Checkout complement
-      - name: "Set Go Version"
-        run: |
-          echo "$GOROOT_1_17_X64/bin" >> $GITHUB_PATH
-          echo "~/go/bin" >> $GITHUB_PATH
+      - uses: actions/setup-go@v4
       - name: "Install Complement Dependencies"
-        # We don't need to install Go because it is included on the Ubuntu 20.04 image:
-        # See https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-Readme.md specifically GOROOT_1_17_X64
         run: |
           sudo apt-get update && sudo apt-get install -y libolm3 libolm-dev
       - name: "Run internal Complement tests"
@@ -55,20 +50,12 @@ jobs:
     steps:
       - uses: actions/checkout@v2 # Checkout complement
 
-      # Env vars are set file a file given by $GITHUB_PATH. We need both Go 1.17 and GOPATH on env.
-      # See https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#adding-a-system-path
-      - name: "Set Go Version"
-        run: |
-          echo "$GOROOT_1_17_X64/bin" >> $GITHUB_PATH
-          echo "~/go/bin" >> $GITHUB_PATH
-
+      - uses: actions/setup-go@v4
       # Similar steps as dockerfiles/ComplementCIBuildkite.Dockerfile but on the host. We need
       # to do this so we can _be_ the host when running Complement so we can snaffle all the ports. If
       # we run Complement _in_ Docker then we can't -p all high numbered ports which then breaks federation
       # servers which listen on random high numbered ports.
       - name: "Install Complement Dependencies"
-        # We don't need to install Go because it is included on the Ubuntu 20.04 image:
-        # See https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-Readme.md specifically GOROOT_1_17_X64
         run: |
           sudo apt-get update && sudo apt-get install -y libolm3 libolm-dev
           go get -v github.com/gotesttools/gotestfmt/v2/cmd/gotestfmt@latest