GHA: Remove -gcflags="-m" from go build

According to "go tool compile", the "-m" flag results in "print[ing]
optimization decisions". Those are shown on GitHub PRs as errors.

In my opinion, this behavior is misleading and has no real benefit.

.github/workflows/go.yml

@@ -21,7 +21,7 @@ jobs:
         with:
           go-version: 1.x
 
-      - run: go build -gcflags="-m" ./...
+      - run: go build ./...
 
       - run: go test -v -race ./...