gh-39670: CI: Remove broken Linux Mint and openSUSE runs
    
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Remove the following broken CI runs
(https://github.com/sagemath/sage/actions/runs/13750937379):
- Linux Mint: fails due to an error in the retrofit script
   ```
   touch: cannot touch 'build/make/Makefile': No such file or directory
   rm: cannot remove '/new/.git': Directory not empty
   ```
- openSUSE with python 3.10 fails with `checking ... whether
/usr/bin/python3.10 is good... no, Python 3.10.16 is too old`
   can probably be removed compltely; at least sage-lib no longer
supports 3.10, not sure about sage-the-distro.

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URL: #39670
Reported by: Tobias Diez
Reviewer(s): Dima Pasechnik

Author: Release Manager

.github/workflows/docker.yml

@@ -23,20 +23,13 @@ on:
            "ubuntu-jammy",
            "debian-bullseye",
            "debian-bookworm",
-           "linuxmint-20.2",
-           "linuxmint-20.3",
-           "linuxmint-21",
-           "linuxmint-21.1",
-           "linuxmint-21.2",
-           "linuxmint-21.3",
            "fedora-40",
            "fedora-41",
            "centos-stream-9",
            "centos-stream-9-python3.12",
            "almalinux-9-python3.11",
            "archlinux-latest",
            "opensuse-15.5-gcc_11-python3.11",
-           "opensuse-tumbleweed-python3.10",
            "opensuse-tumbleweed",
           ]
         # 'tox -e update_docker_platforms' updates above