MDL-75726 ci: Bump GHA to Ubuntu 22.04

Have tried to also bump Travis to 22.04 (jammy) but it
was not working ok, with problems trying to find both
PHP and PostgreSQL versions.

Surely that's because 22.04 support is really new (Sep 9, 2022):

https://blog.travis-ci.com/22-9-9-ubuntujammy

So we'll have to wait a little more before being able to, also,
bump Travis to use 22.04

.github/workflows/push.yml

@@ -13,7 +13,7 @@ env:
 
 jobs:
   Grunt:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     steps:
       - name: Checking out code
@@ -54,11 +54,11 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-20.04
+          - os: ubuntu-22.04
             php: 7.3
             extensions:
             db: mysqli
-          - os: ubuntu-20.04
+          - os: ubuntu-22.04
             php: 8.0
             db: pgsql
             extensions: xmlrpc-beta