fix(ci): use ubuntu-latest for mypy action (#2784)

.github/workflows/mypy.yaml

diff --git a/.github/workflows/mypy.yaml b/.github/workflows/mypy.yaml
index 866c43a..e774b9b 100644
--- a/.github/workflows/mypy.yaml
+++ b/.github/workflows/mypy.yaml
@@ -15,7 +15,7 @@
 
 jobs:
   ci:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
       # Checkout the code
       - uses: actions/checkout@v4