Revert ADO pipelines to Ubuntu 22.04 temporarily (microsoft#7365)

DXC seems to be building inocrrectly with GCC-13 and later, which is
causing our pre-merge testing on 24.04 to fail. This will take some time
to sort out, so in the meantime I'm reverting to 22.04 on our pipelines.

Author: llvm-beanz

azure-pipelines.yml

@@ -54,7 +54,7 @@ stages:
 
     variables:
       macOS: macOS-latest
-      linux: Ubuntu-latest
+      linux: Ubuntu-22.04 # FIXME: #7364, DXC does not build correctly with GCC 13+
 
     strategy:
       matrix: