[misc] Move the FreeBSD port test to release 15.1 (#7999)

* [misc] Move the FreeBSD port test to release 15.1

FreeBSD 15.0 reached end of life on 2026-09-30 and the ports tree marks
it unsupported since freebsd/freebsd-ports@ed90b23fe9 (2026-10-01), so
`make package` refuses to run on the 15.0 VM and the FreeBSD Port job
fails on every PR. The pinned vmactions/freebsd-vm v1.4.8 ships a 15.1
image, so only the release needs to move.

* [misc] Run the FreeBSD unit tests on release 15.1 too

The job installs binary packages instead of building from the ports
tree, so it kept passing on the EOL 15.0 image, but the client should
be tested on the same supported release the port is built on, and the
EOL image is only served from the archive mirror from now on.

.github/workflows/release.yml

@@ -69,7 +69,7 @@ jobs:
         with:
           usesh: true
           copyback: false
-          release: "15.0"
+          release: "15.1"
           envs: "GO_VERSION"
           prepare: |
             # Install required packages