Fix RC CI: JNI macos-15 aarch_64 fails with missing utf8_validity.h #1408

The JNI macos-15 aarch_64 job in the RC workflow has failed on every push to main since 2026-10-26 ~07:53 UTC.

The Gandiva JNI build fails with:

protobuf-src/src/google/protobuf/parse_context.h:43:10: fatal error: 'utf8_validity.h' file not found

The workflow builds against apache/arrow main, whose bundled protobuf went from v31.1 to v36.2. protobuf v36.2's parse_context.h includes utf8_validity.h directly, which lives in third_party/utf8_range of the bundled protobuf source. That directory is not on the Gandiva JNI include path, similar to the bundled Abseil headers handled in #1264.