Bump bundle cache version

This'll ensure a clean action run; I noticed in the previous commit the job outputted "Cache restored successfully" which may have given us a false positive success.

.github/workflows/main.yml

@@ -23,5 +23,6 @@ jobs:
       with:
         ruby-version: ${{ matrix.ruby }}
         bundler-cache: true
+        cache-version: 1
     - name: Run the default task
       run: bundle exec rake