Bump Ubuntu 20.04 CI to 22.04

The 20.04 is no longer available

Author: bukka

.github/workflows/ci.yml

@@ -8,9 +8,9 @@ on:
   pull_request:
 
 jobs:
-  linux_ubuntu_20:
-    name: Linux Ubuntu 20.04 (${{ matrix.backend }})
-    runs-on: ubuntu-20.04 # for OpenSSL 1.1.1 and Botan 2.12
+  linux_ubuntu_22:
+    name: Linux Ubuntu 22.04 (${{ matrix.backend }})
+    runs-on: ubuntu-22.04 # for OpenSSL 3.0.2
     strategy:
       fail-fast: false
       matrix:
@@ -36,7 +36,7 @@ jobs:
 
   linux_ubuntu_24:
     name: Linux Ubuntu 24.04 (${{ matrix.backend }})
-    runs-on: ubuntu-24.04 # for OpenSSL 3.0 and Botan 2.19
+    runs-on: ubuntu-24.04 # for OpenSSL 3.0.13
     strategy:
       fail-fast: false
       matrix: