Downgrade build-minimum CI job Ubuntu version

Our build-minimum workflow started failing because ubuntu-latest is now
Ubuntu 24.04 and it does not come with a static libreadline installed by
default (or so).
Switch back to 22.04 to bring things back to working.

.github/workflows/test.yml

@@ -1,4 +1,4 @@
-# Copyright (C) 2022-2024 Daniel Mueller <[email protected]>
+# Copyright (C) 2022-2025 Daniel Mueller <[email protected]>
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 name: Test
@@ -38,7 +38,7 @@ jobs:
         cargo build --profile=${{ matrix.profile }} --bins --tests --examples --features=test
   build-minimum:
     name: Build using minimum versions of dependencies
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
       - name: Install Nightly Rust