[x15sr71]

In raising this pull request, I confirm the following (please check boxes):

Reason for this PR:

• This PR adds new functionality.
• This PR fixes a bug that I have personally experienced or that a real user has reported and for which a sample exists.
• This PR is porting code from C to Rust.

Sanity check:

• I have read and understood the contributors guide.
• I have checked that another pull request for this purpose does not exist.
• If the PR adds new functionality, I've added it to the changelog. If it's just a bug fix, I have NOT added it to the changelog.
• I am NOT adding new C code unless it's to fix an existing, reproducible bug.

---

Problem

Since 2026-10-24, ubuntu-latest runs Ubuntu 26.04, and every PR's Linux CI fails before anything is built. Example: #2427's run:

• Build CCExtractor on Linux: all 7 jobs stop at the dependency step with E: Package 'libgpac-dev' has no installation candidate. Ubuntu 26.04 doesn't ship GPAC (#2254).
• Format: the newer clang-format on 26.04 wants to reformat files the PR doesn't touch (ccx_decoders_isdb.c, mp4.c).

The same runs passed on 2026-10-23, on the ubuntu-24.04 image.

Fix

Pin runs-on to ubuntu-24.04 in build_linux.yml (7 jobs) and format.yml (2 jobs). build_deb.yml is already pinned to ubuntu-24.04 the same way.

The other workflows on ubuntu-latest don't install GPAC, or build inside a container (build_deb_debian13.yml), so they aren't affected.

Testing

• Build CCExtractor on Linux: GitHub Actions run on my fork. All 7 jobs pass on ubuntu-24.04, installing libgpac-dev 2.2.1.
• Format: this workflow only runs on pull requests, so I ran its two commands in an ubuntu:24.04 container (clang-format 18.1.3) on this branch and on [FIX] telxcc: don't close the current page when another subtitle page's header arrives #2427. No changes in either.

This keeps CI working until GPAC on 26.04 is sorted out (#2254, #2320).