Fix lite classes in the protobuf-java Maven release to be JDK8 compatible.

Adds LITE_SRCS to core_bundle which seems to be sufficient to ensure these are compiled targeting Java 8 in //java/core:core_mvn Bazel 7. Note this changes the output of `//java/core:core_bundle`, which should only be used for `//java/core:core_mvn` anyways.

This seems to have been broken originally by commit (https://github.com/protocolbuffers/protobuf/commit/c820dd0ca69b19b142fc9d8a6635530b5a5fc93b) when using bazel 7 image.

Fixes https://github.com/protocolbuffers/protobuf/issues/20580

PiperOrigin-RevId: 740760724