Tweak lcov commands to not delete everything

.github/workflows/cron-ci.yaml

@@ -45,8 +45,9 @@ jobs:
             local tool=$1; shift; "$(rustc --print target-libdir)/../bin/llvm-$tool" "$@"
           }
           rusttool profdata merge extra_tests/snippet-*.profraw regrtest.profraw --output codecov.profdata
-          rusttool cov export --instr-profile codecov.profdata target/release/rustpython --format lcov >codecov.lcov
-          lcov -r codecov.lcov '/*' -o codecov.lcov
+          rusttool cov export --instr-profile codecov.profdata target/release/rustpython --format lcov > codecov_tmp.lcov
+          lcov -e codecov_tmp.lcov "$PWD"/'*' -o codecov_tmp2.lcov
+          lcov -r codecov_tmp2.lcov "$PWD"/target/'*' -o codecov.lcov  # remove LALRPOP-generated parser
       - name: upload to Codecov
         uses: codecov/codecov-action@v3
         with: