Use ubuntu-22.04 for Linux-legacy CI runs since GitHub has retired ubuntu-20.04

Author: mikke89

.github/workflows/build.yml

@@ -51,7 +51,7 @@ jobs:
 
 
   Linux-legacy:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     env:
       BUILD_TYPE: Release