Bump our Ubuntu runners (#2168)

chore: No supported no moar :((

.github/workflows/testing.yml

@@ -40,15 +40,15 @@ jobs:
   unix:
     strategy:
       matrix:
-        os: [ubuntu-22.04, macos-15-intel, macos-26]
+        os: [ubuntu-24.04, ubuntu-26.04-arm, macos-15-intel, macos-26]
         cxx: [g++, clang++]
         buildsys: [make, cmake]
         exclude: # Don't use `g++` on macOS; it's just an alias to `clang++`.
           - { os: macos-15-intel, cxx: g++ }
           - { os: macos-26, cxx: g++ }
         include: # Use `g++-10`, the earliest GCC version we support, on the earliest Ubuntu runner.
-          - { os: ubuntu-22.04, cxx: g++-10, buildsys: make }
-          - { os: ubuntu-22.04, cxx: g++-10, buildsys: cmake }
+          - { os: ubuntu-24.04, cxx: g++-10, buildsys: make }
+          - { os: ubuntu-24.04, cxx: g++-10, buildsys: cmake }
       fail-fast: false
     runs-on: ${{ matrix.os }}
     steps: