Avoid Unix specifics on Windows.
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 56b4874..5e20f9a 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -21,7 +21,7 @@
       - name: configure
         working-directory: ${{runner.workspace}}/build
         run: |
-          cmake $GITHUB_WORKSPACE
+          cmake ..
       - name: build
         working-directory: ${{runner.workspace}}/build
         run: |