Fix spec job to include :spec bundle group

Author: tobi

.github/workflows/liquid.yml

@@ -44,6 +44,8 @@ jobs:
 
   spec:
     runs-on: ubuntu-latest
+    env:
+      BUNDLE_WITH: spec
     steps:
       - uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
       - uses: ruby/setup-ruby@a25f1e45f0e65a92fcb1e95e8847f78fb0a7197a # v1.273.0