Set BUNDLE_WITHOUT for the whole test job

It was set only while installing, so bundle exec went on to demand the
sig group that install had just 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
@@ -26,8 +28,6 @@ jobs:
         ruby-version: ${{ matrix.ruby }}
     - name: Install dependencies
       run: bundle install
-      env:
-        BUNDLE_WITHOUT: sig
     - name: Run test
       run: bundle exec rake test
     - name: Build