Package regexp fails to build with OpenJDK 21 in RHEL 10.
The reason is that it uses Java compiler source/target/release lower
than 1.8, which is the minimum supported by OpenJDK 21.

Affected NVR: regexp-1.5-46.el10

The fix is to bump regexp source/target/release to 1.8 or higher.

Acceptance criteria: package regexp builds fine in RHEL 10.

Test coverage: not needed.