Fix CI by ensuring gotestfmt is on PATH, plus cleanups (#634)

* 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.

* Bump checkout action

Drive-by fix for matrix-org/synapse#14203

* Check that gotestfmt is installed

no `-version` flag, so `help` will have to do

* `go install gotestfmt` instead of `go get`

IDK why this suddenly started failing, but `go install` seems to put it
on the PATH in a way that makes CI work.

.github/workflows/ci.yaml

@@ -14,14 +14,9 @@ jobs:
   complement-internal:
     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/checkout@v3 # Checkout complement
+      - 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"
@@ -53,27 +48,20 @@ jobs:
             timeout: 10m
 
     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/checkout@v3 # Checkout complement
 
+      - 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
+          go install -v github.com/gotesttools/gotestfmt/v2/cmd/gotestfmt@latest
           mkdir .gotestfmt/github -p
           cp .ci/complement_package.gotpl .gotestfmt/github/package.gotpl
+          gotestfmt -help
 
       - name: "Checkout corresponding ${{ matrix.homeserver }} branch"
         shell: bash