use rack-plugin-toolchain-dir env variable

Author: qno

.github/workflows/build-plugin.yml

@@ -1,6 +1,9 @@
 name: Build VCV Rack Plugin
 on: [push, pull_request]
 
+env:
+  rack-plugin-toolchain-dir: /home/build/rack-plugin-toolchain
+
 defaults:
   run:
     shell: bash
@@ -30,12 +33,12 @@ jobs:
       - name: Build plugin
         run: |
           export PLUGIN_DIR=$GITHUB_WORKSPACE
-          pushd /home/build/rack-plugin-toolchain
+          pushd ${{ env.rack-plugin-toolchain-dir }}
           make plugin-build-${{ matrix.platform }}
       - name: Upload artifact
         uses: actions/upload-artifact@v2
         with:
-          path: /home/build/rack-plugin-toolchain/plugin-build
+          path: ${{ env.rack-plugin-toolchain-dir }}/plugin-build
           name: ${{ matrix.platform }}
 
   publish: