migrate mypy to ubuntu-latest

Author: aignas

.github/workflows/mypy.yaml

@@ -1,3 +1,4 @@
+---
 name: mypy
 
 on:
@@ -15,7 +16,7 @@ defaults:
 
 jobs:
   ci:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
       # Checkout the code
       - uses: actions/checkout@v4