ci: fix empty RELEASE_FLAG causing incorrect arg parsing

When RELEASE_FLAG env var was empty, bash treated it as an empty
string argument rather than removing it, shifting the positional
args. Inline the GitHub Actions expression instead.

Author: flavorjones

.github/workflows/build-gems.yml

@@ -57,9 +57,7 @@ jobs:
         with:
           ruby-version: "4.0"
           bundler-cache: true
-      - run: ./bin/test-gem-build ${RELEASE_FLAG} gems ruby
-        env:
-          RELEASE_FLAG: ${{ inputs.release && '--release' || '' }}
+      - run: ./bin/test-gem-build ${{ inputs.release && '--release' || '' }} gems ruby
       - uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
         with:
           name: "${{ inputs.artifact_prefix }}source-gem"
@@ -97,10 +95,9 @@ jobs:
       - run: |
           docker run --rm -v $PWD:/work -w /work \
             ghcr.io/rake-compiler/rake-compiler-dock-image:${RCD_IMAGE_VERSION}-mri-${{ matrix.platform }} \
-            ./bin/test-gem-build ${RELEASE_FLAG} gems ${{ matrix.platform }}
+            ./bin/test-gem-build ${{ inputs.release && '--release' || '' }} gems ${{ matrix.platform }}
         env:
           RCD_IMAGE_VERSION: ${{ needs.native_setup.outputs.rcd_image_version }}
-          RELEASE_FLAG: ${{ inputs.release && '--release' || '' }}
       - uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
         with:
           name: "${{ inputs.artifact_prefix }}cruby-${{ matrix.platform }}-gem"