ga: use a different magic value for the workspace

.github/workflows/continuous-integration.yml

diff --git a/.github/workflows/continuous-integration.yml b/.github/workflows/continuous-integration.yml
index ca768b8..68bc100 100644
--- a/.github/workflows/continuous-integration.yml
+++ b/.github/workflows/continuous-integration.yml
@@ -17,7 +17,7 @@
       - name: configure
         working-directory: ${{runner.workspace}}/build
         run: |
-          cmake ${{runner.workspace}}
+          cmake $GITHUB_WORKSPACE
       - name: build
         working-directory: ${{runner.workspace}}/build
         run: |