Rename tests/sanity.py to tests/checkers.py (#563)

This change renames tests/sanity.py -> tests/checkers.py.

The term sanity is not very clear and potentially offensive, and it's
already used by `ansible-test sanity` to mean something different.

Fixes: https://github.com/ansible/ansible-documentation/issues/530

.github/workflows/ci.yaml

@@ -29,9 +29,9 @@ jobs:
       run: |
         python docs/bin/clone-core.py
 
-    - name: Run docs-build Sanity
+    - name: Run docs-build Checkers
       run: |
-        python tests/sanity.py docs-build
+        python tests/checkers.py docs-build
 
   docs_sanity_rstcheck:
     name: rstcheck
@@ -53,9 +53,9 @@ jobs:
       run: |
         python docs/bin/clone-core.py
 
-    - name: Run rstcheck Sanity
+    - name: Run rstcheck Checkers
       run: |
-        python tests/sanity.py rstcheck
+        python tests/checkers.py rstcheck
 
   nox:
     uses: ./.github/workflows/reusable-nox.yml