Rename test job

This renames the test job to "test" which I think is more descriptive,
and also matches the new required-ci checks name.

Author: ehuss

.github/workflows/test.yml

@@ -4,7 +4,7 @@ on:
 
 jobs:
   test:
-    name: CI
+    name: test
     runs-on: ubuntu-latest
     env:
       MDBOOK_VERSION: 0.4.51