lock bundler to <4 in CI for now, engine_cart incompatibility

Author: jrochkind

.github/workflows/ruby.yml

@@ -22,6 +22,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        # Bundler locked to <4, see https://github.com/projectblacklight/blacklight_range_limit/pull/328
+        bundler: "2.7.2"
+
         # We have SEVERAL axes of difference we support.
         #
         #   * Blacklight: 7, 8, or 9