ci: use latest bundler

ruby 2.5 just started failing

Author: flavorjones

.github/workflows/ci-test.yml

@@ -42,6 +42,7 @@ jobs:
       with:
         ruby-version: ${{matrix.ruby-version}}
         bundler-cache: true
+        bundler: latest
     - run: bundle exec rake test
 
   test-platform:
@@ -58,4 +59,5 @@ jobs:
       with:
         ruby-version: "3.2"
         bundler-cache: true
+        bundler: latest
     - run: bundle exec rake test