ci: Pin dotnet and codgen workflows to Ubuntu 22.04

- Dotnet workflows currently failing on Ubuntu 24.04

Author: kieran-ryan

.github/workflows/test-codegen.yml

@@ -12,7 +12,7 @@ on:
 
 jobs:
   test-codegen:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
 
     steps:
       - uses: actions/checkout@v4

.github/workflows/test-dotnet.yml

@@ -20,7 +20,7 @@ on:
 
 jobs:
   test-dotnet:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-dotnet@v4