CI: Bust the macOS Lagom ccache and reduce its size

It currently takes upwards of 40 minutes to download the ccache on macOS
and often errors-out near the end. Change the cache version to bust it
so we can start anew. Reduce its max size to 2 GB (a clean build is ~0.9
GB, so this allows just over 2 clean builds to be cached).

Meta/Azure/Lagom.yml

@@ -45,6 +45,9 @@ jobs:
         ${{ if eq(parameters.os, 'Android') }}:
           with_ndk_cache: true
           ndk_version: '$(ndk_version)'
+        ${{ if eq(parameters.os, 'macOS') }}:
+          ccache_version: 2
+          serenity_ccache_size: '2G'
 
     - ${{ if eq(parameters.os, 'Android') }}:
       - script: |