Update manylinux build action

Author: jim-easterbrook

.github/workflows/build-manylinux.yml

@@ -47,7 +47,7 @@ jobs:
 
   test:
     needs: build
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         python-version: ['3.6', '3.7', '3.8', '3.9', '3.10']