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

@@ -58,7 +58,7 @@ jobs:
       - name: "Install Complement Dependencies"
         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