CI: Attempt to satisfy Windows when invoking "bin/coverage"

Author: amotl

.github/workflows/main.yml

@@ -60,6 +60,6 @@ jobs:
 
           test_program=bin/test
           if [[ ${{ matrix.os }} = "macos-latest" || ${{ matrix.os }} = "windows-latest" ]]; then
-            test_program=bin/test-quick
+            test_program=$(which bin/test-quick)
           fi
           bin/coverage run $test_program -vv1