Test using 22.04 again

Locally using 22.04 + PHP 8.1 + OpenSSL 3 I don't get the error we
were getting in CI previously. Trying this again to see if this problem
has been resolved by changes in PHP and OpenSSL.

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ on:
 
 jobs:
   testsuite:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
       matrix: