Store Go version as a step output

This changes from using an environment variable to using a step output to store
the Go version that is installed. This mirrors changes made to the other
program versions and how they're stored.

.github/workflows/build.yml

@@ -24,16 +24,16 @@ jobs:
         uses: actions/setup-python@v2
         with:
           python-version: 3.9
-      # GO_VERSION and GOCACHE are used by the cache task, so the Go
-      # installation must happen before that.
+      # We need the Go version and Go cache location for the actions/cache step,
+      # so the Go installation must happen before that.
       - uses: actions/setup-go@v2
         with:
           go-version: '1.16'
       - name: Store installed Go version
+        id: go-version
         run: |
-          echo "GO_VERSION="\
-          "$(go version | sed 's/^go version go\([0-9.]\+\) .*/\1/')" \
-          >> $GITHUB_ENV
+          echo "::set-output name=version::"\
+          "$(go version | sed 's/^go version go\([0-9.]\+\) .*/\1/')"
       - name: Lookup Go cache directory
         id: go-cache
         run: |
@@ -42,7 +42,7 @@ jobs:
         env:
           BASE_CACHE_KEY: "${{ github.job }}-${{ runner.os }}-\
             py${{ steps.setup-python.outputs.python-version }}-\
-            go${{ env.GO_VERSION }}-\
+            go${{ steps.go-version.outputs.version }}-\
             packer${{ steps.setup-env.outputs.packer-version }}-\
             tf${{ steps.setup-env.outputs.terraform-version }}-"
         with: