CI: Fix XMAKE_GLOBALDIR on Windows

.github/workflows/coverage.yml

@@ -48,9 +48,14 @@ jobs:
         choco install -y OpenCppCoverage
 
     # Force xmake to a specific folder (for cache)
-    - name: Set xmake env
+    - name: Set xmake env (Linux)
+      if: runner.os == 'Linux'
       run: echo "XMAKE_GLOBALDIR=${{ runner.workspace }}/xmake-global" >> $GITHUB_ENV
 
+    - name: Set xmake env (Windows)
+      if: runner.os == 'Windows'
+      run: echo "XMAKE_GLOBALDIR=${{ runner.workspace }}/xmake-global" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+
     # Install xmake
     - name: Setup xmake
       uses: xmake-io/github-action-setup-xmake@v1