ci(fix): cache all dependencies installed by bundler (#372)

Author: pkuczynski

.github/workflows/tests.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       COVERAGE_RUBY_VERSION: 2.6
-      BUNDLE_PATH: vendor/bundle
+      BUNDLE_PATH: ${{ github.workspace }}/vendor/bundle
     strategy:
       fail-fast: false
       matrix: