ci: make use of caching in actions/setup-go

The GH action to set up Golang (actions/setup-go) has cache
functionality. For cache hits, this saves ~2 minutes for each run. In
order for the cache to hit, caching must not be disabled, and the code
must be checked out before setting up Golang.

Signed-off-by: Blaine Gardner <blaine.gardner@ibm.com>

.github/workflows/codegen.yml

@@ -29,15 +29,15 @@ jobs:
     runs-on: ubuntu-20.04
     if: "!contains(github.event.pull_request.labels.*.name, 'skip-ci')"
     steps:
-      - uses: actions/setup-go@v4
-        with:
-          go-version: "1.21"
-
       - name: checkout
         uses: actions/checkout@v4
         with:
           fetch-depth: 0
 
+      - uses: actions/setup-go@v4
+        with:
+          go-version: "1.21"
+
       - name: run codegen
         run: GOPATH=$(go env GOPATH) make codegen