Small CI improvements (#1703)

* Disable `fast-fail`

Since we test against multiple versions of Ruby it makes sense to allow all Rubies to finish, regardless of fails for specific versions.

* Run test workflow for all branches

.github/workflows/test.yml

@@ -10,14 +10,15 @@ name: Testing
 on:
   push:
     branches:
-      - master
+      - '**'
   pull_request:
 
 jobs:
   test:
     name: Test with Ruby-${{ matrix.ruby }}
     runs-on: ubuntu-latest
     strategy:
+      fail-fast: false
       matrix:
         # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
         # TODO: Add jruby if something like allow_failures will be implemented on Actions.