ci: mitigate template injection attack in build_linux_wheel (#3195)

This patch mitigates template injection vulnerabilities in GitHub
Workflows by replacing direct references with an environment variable.

Aikido used AI to generate this PR.

High confidence: Aikido has a robust set of benchmarks for similar
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Co-authored-by: aikido-autofix[bot] <119856028+aikido-autofix[bot]@users.noreply.github.com>

.github/workflows/build_linux_wheel/action.yml

@@ -23,8 +23,10 @@ runs:
   steps:
     - name: CONFIRM ARM BUILD
       shell: bash
+      env:
+        ARM_BUILD: ${{ inputs.arm-build }}
       run: |
-        echo "ARM BUILD: ${{ inputs.arm-build }}"
+        echo "ARM BUILD: $ARM_BUILD"
     - name: Build x86_64 Manylinux wheel
       if: ${{ inputs.arm-build == 'false' }}
       uses: PyO3/maturin-action@v1