ci: Fix build caching on Windows (#4811)

* ci: Fix build caching on Windows

I was getting tired of Windows being slow as molasses in our CI jobs, so I went to look at our trusty source of github actions + golang information, and found a somewhat recent commit that actually fixed it. See 4b754729ba

I'll do a 2nd empty commit to re-trigger CI shortly to confirm that it actually fixes it.

* Retrigger CI

.github/workflows/ci.yml

@@ -78,12 +78,20 @@ jobs:
         printf "Git version: $(git version)\n\n"
         # Calculate the short SHA1 hash of the git commit
         echo "::set-output name=short_sha::$(git rev-parse --short HEAD)"
-        echo "::set-output name=go_cache::$(go env GOCACHE)"
 
     - name: Cache the build cache
       uses: actions/cache@v2
       with:
-        path: ${{ steps.vars.outputs.go_cache }}
+        # In order:
+        # * Module download cache
+        # * Build cache (Linux)
+        # * Build cache (Mac)
+        # * Build cache (Windows)
+        path: |
+          ~/go/pkg/mod
+          ~/.cache/go-build
+          ~/Library/Caches/go-build
+          ~\AppData\Local\go-build
         key: ${{ runner.os }}-${{ matrix.go }}-go-ci-${{ hashFiles('**/go.sum') }}
         restore-keys: |
           ${{ runner.os }}-${{ matrix.go }}-go-ci