Use env. variable instead of an expression in action.yml (fixes #7)

This is a workaround for backslashes being included in the path for
${{ github.action_path }} even when using bash on Windows.

action.yml

@@ -217,7 +217,7 @@ runs:
         echo ::group::Create Qlot Environment
 
         if [[ -n "${QLFILE_TEMPLATE}" ]]; then
-            echo "${QLFILE_TEMPLATE}" | ${{ github.action_path }}/templater.ros > qlfile
+            echo "${QLFILE_TEMPLATE}" | $GITHUB_ACTION_PATH/templater.ros > qlfile
             rm -f qlfile.lock
         fi