ci: move input interpolation into an intermediate environment variable

best practice according to: https://docs.github.com/en/actions/reference/security/secure-use#use-an-intermediate-environment-variable

Author: typfel

.github/actions/make/action.yml

@@ -40,10 +40,13 @@ runs:
     - name: compute artifact key
       shell: bash -euo pipefail {0}
       id: compute-key
+      env:
+        INPUTS_KEY: ${{ inputs.key }}
+        MAKE_RULE: ${{ inputs.make-rule }}
       run: |
-        files_hash=$($MAKE "${{ inputs.make-rule }}"-hash-deps)
+        files_hash=$($MAKE "${MAKE_RULE}"-hash-deps)
         # Change the ARTIFACT_GENERATION repository variable to force fresh artifacts
-        echo "key=${{ inputs.key }}-$files_hash-${{ inputs.artifact-generation }}" >> "$GITHUB_OUTPUT"
+        echo "key=${INPUT_KEY}-$files_hash-${{ inputs.artifact-generation }}" >> "$GITHUB_OUTPUT"
     - name: branch name
       id: branch-name
       run: |