gh-36282: CI: Remove ubuntu-kinetic (defunct)
    
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This non-LTS release can no longer be tested.

https://github.com/sagemath/sage/actions/runs/6207962004/job/16853655527
#step:8:60
```
E: The repository 'http://security.ubuntu.com/ubuntu kinetic-security
Release' does not have a Release file.
E: The repository 'http://archive.ubuntu.com/ubuntu kinetic Release'
does not have a Release file.
E: The repository 'http://archive.ubuntu.com/ubuntu kinetic-updates
Release' does not have a Release file.
E: The repository 'http://archive.ubuntu.com/ubuntu kinetic-backports
Release' does not have a Release file.
```
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URL: #36282
Reported by: Matthias Köppe
Reviewer(s): Dima Pasechnik

Author: Release Manager

.github/workflows/ci-linux.yml

@@ -82,7 +82,6 @@ jobs:
       # Only test systems with a usable system python (>= 3.9)
       tox_system_factors: >-
         ["ubuntu-jammy",
-         "ubuntu-kinetic",
          "ubuntu-lunar",
          "ubuntu-mantic",
          "debian-bullseye",

.github/workflows/docker.yml

@@ -21,7 +21,6 @@ on:
            "ubuntu-bionic-gcc_8",
            "ubuntu-focal",
            "ubuntu-jammy",
-           "ubuntu-kinetic",
            "ubuntu-lunar",
            "ubuntu-mantic",
            "debian-buster-gcc_spkg",

tox.ini

@@ -220,8 +220,6 @@ setenv =
     ubuntu-bionic:                             IGNORE_MISSING_SYSTEM_PACKAGES=yes
     ubuntu-focal:     BASE_TAG=focal
     ubuntu-jammy:     BASE_TAG=jammy
-    ubuntu-kinetic:   BASE_TAG=kinetic
-    ubuntu-kinetic:                            IGNORE_MISSING_SYSTEM_PACKAGES=yes
     ubuntu-lunar:     BASE_TAG=lunar
     ubuntu-lunar:                              IGNORE_MISSING_SYSTEM_PACKAGES=yes
     ubuntu-mantic:    BASE_TAG=mantic