Use --preserve-paths for gcov and fix gcov_include

Author: skirpichev

.github/workflows/coverage.yml

@@ -83,9 +83,6 @@ jobs:
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           gcov_ignore: pythoncapi_compat.h
-          gcov_include: fmt.c
-                        gmp.c
-                        libzz/zz.c
-                        utils.c
-          gcov_args: --no-external
+          gcov_include: '*.c, libzz/*.c'
+          gcov_args: --no-external --preserve-paths
           fail_ci_if_error: true