Run the tests through bundle exec

Without it the tests load whatever net/protocol the Ruby ships rather
than the net-protocol the gemspec requires, so on Ruby 2.7, where
net/protocol is plain stdlib and not a default gem, readuntil has no
limit keyword. BUNDLE_WITHOUT moves to the job so that bundle exec does
not then demand the sig group install skipped.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: hsbt

.github/workflows/test.yml

@@ -18,6 +18,8 @@ jobs:
         ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
         os: [ ubuntu-latest, macos-latest, windows-latest ]
     runs-on: ${{ matrix.os }}
+    env:
+      BUNDLE_WITHOUT: sig
     steps:
     - uses: actions/checkout@v7
     - name: Set up Ruby
@@ -26,11 +28,9 @@ jobs:
         ruby-version: ${{ matrix.ruby }}
     - name: Install dependencies
       run: bundle install
-      env:
-        BUNDLE_WITHOUT: sig
     - name: Run test
-      run: rake test
+      run: bundle exec rake test
     - name: Build
-      run: rake build
+      run: bundle exec rake build
       env:
         LANG: C