Remove mysql from apt repository sources for catalog due to expired key

[AetherUnbound]

Description

This PR fixes a critical issue that's causing CI on main to fail when building the catalog (example run: https://github.com/WordPress/openverse/actions/runs/7213002475).

It seems the MySQL PGP key may be expired, and that's causing fresh builds of the catalog to fail. The build log failure we're seeing is:

 > [scheduler 2/7] RUN apt-get update     && apt-get -yqq install       build-essential       libpq-dev       libffi-dev     && apt-get autoremove -y     && rm -rf /var/lib/apt/lists/*:
0.538 Get:1 http://deb.debian.org/debian bullseye InRelease [116 kB]
0.580 Get:2 http://deb.debian.org/debian-security bullseye-security InRelease [48.4 kB]
0.595 Get:3 http://deb.debian.org/debian bullseye-updates InRelease [44.1 kB]
0.677 Get:4 http://deb.debian.org/debian bullseye/main amd64 Packages [8062 kB]
0.696 Get:5 https://packages.microsoft.com/debian/11/prod bullseye InRelease [3649 B]
0.715 Get:6 http://repo.mysql.com/apt/debian bullseye InRelease [17.9 kB]
0.957 Get:7 https://packages.microsoft.com/debian/11/prod bullseye/main all Packages [1214 B]
1.002 Err:6 http://repo.mysql.com/apt/debian bullseye InRelease
1.002   The following signatures were invalid: EXPKEYSIG 467B942D3A79BD29 MySQL Release Engineering <mysql-build@oss.oracle.com>
1.049 Get:8 https://packages.microsoft.com/debian/11/prod bullseye/main amd64 Packages [131 kB]
1.113 Get:9 https://packages.microsoft.com/debian/11/prod bullseye/main arm64 Packages [27.5 kB]
1.137 Get:10 https://packages.microsoft.com/debian/11/prod bullseye/main armhf Packages [24.9 kB]
1.181 Get:11 http://deb.debian.org/debian-security bullseye-security/main amd64 Packages [260 kB]
1.191 Get:12 http://deb.debian.org/debian bullseye-updates/main amd64 Packages [17.7 kB]
1.442 Get:13 https://apt.postgresql.org/pub/repos/apt bullseye-pgdg InRelease [123 kB]
2.014 Get:14 https://apt.postgresql.org/pub/repos/apt bullseye-pgdg/main amd64 Packages [305 kB]
2.293 Reading package lists...
2.801 W: GPG error: http://repo.mysql.com/apt/debian bullseye InRelease: The following signatures were invalid: EXPKEYSIG 467B942D3A79BD29 MySQL Release Engineering <mysql-build@oss.oracle.com>
2.801 E: The repository 'http://repo.mysql.com/apt/debian bullseye InRelease' is not signed.

Since we do not use MySQL in our Airflow setup, we should be safe to exclude this source from the list when running apt during image building. I've tested this locally and it appears to work fine!

Testing Instructions

CI/CD passing should be a positive indicator!

1. On the main branch, run just dc pull then just build scheduler --no-cache
2. Observe that the build error occurs
3. Check out this branch and run just build scheduler --no-cache, this should now succeed

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.
• I ran the DAG documentation generator (if applicable).

Developer Certificate of Origin

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[dhruvkb]

Can we not remove all sources except the ones we need? That would entirely prevent the problem from reappearing (and potentially make the images slightly smaller).

Approving to unblock as critical, but noted a possible scope for improvement.