Probe GITHUB_PATH

Author: j-woz

.github/workflows/build.yaml

@@ -80,7 +80,11 @@ jobs:
       - name: build swift-t
         run: |
           # For GNU Make:
+          echo GITHUB_PATH $GITHUB_PATH
+          cat $GITHUB_PATH
           echo /opt/homebrew/opt/make/libexec/gnubin >> $GITHUB_PATH
+          cat $GITHUB_PATH
+          ls /opt/homebrew/opt/make/libexec/gnubin
           dev/build/build-swift-t.sh -vv
 
       # TODO check swift-t install