There doesn't seem to be a way to exclude corpora from artifacts

From https://github.com/google/oss-fuzz/pull/7186#issuecomment-1025000134

I think CFLite should pass `UPLOAD_BUILD` to `build_fuzzers` to make it possible to exclude those large corpora from artifacts. Without that environment variable I can't skip that step with something like
```sh
if [[ "$MERGE_WITH_OSS_FUZZ_CORPORA" == "yes" ]]; then

# When the latest builds are uploaded by CFLite the large OSS-Fuzz corpora
# should be excluded regardless of whether MERGE_WITH_OSS_FUZZ_CORPORA
# is set to "yes" or not.
[[ "$UPLOAD_BUILD" == "true" ]] && exit 0
....
```