GitHub: remove Go env variable override

For some reason we used to override the GOCACHE and GOPATH variables
earlier. This now causes the updated cache action not to pick up any
caches. As the overrides shouldn't be needed anymore, we remove them.

.github/actions/setup-go/action.yml

@@ -26,3 +26,8 @@ runs:
         key: ${{ runner.os }}-go-${{ env.GO_VERSION }}-${{ hashFiles('**/go.sum') }}
         restore-keys: |
           ${{ runner.os }}-go-${{ env.GO_VERSION }}-
+
+    - name: set GOPATH
+      shell: bash
+      run: |
+        echo "GOPATH=$(go env GOPATH)" >> $GITHUB_ENV