Update CI.

Author: gkellogg

.github/workflows/ci.yml

@@ -15,6 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       CI: true
+      ALLOW_FAILURES: ${{ endsWith(matrix.ruby, 'head') }}
     strategy:
       fail-fast: false
       matrix:
@@ -42,5 +43,5 @@ jobs:
         with:
           mongodb-version: ${{ matrix.mongodb-version }}
       - name: Run tests
-        run: bundle exec rspec spec
+        run: ruby --version; bundle exec rspec spec || $ALLOW_FAILURES