bpo-40548: Always run GitHub action, even on doc PRs (pythonGH-19981)

Always run GitHub action jobs, even on documentation-only pull
requests. So it will be possible to make a GitHub action job, like
the Windows (64-bit) job, mandatory.

.github/workflows/build.yml

@@ -1,26 +1,19 @@
 name: Tests
 
+# bpo-40548: "paths-ignore" is not used to skip documentation-only PRs, because
+# it prevents to mark a job as mandatory. A PR cannot be merged if a job is
+# mandatory but not scheduled because of "paths-ignore".
 on:
   push:
     branches:
     - master
     - 3.8
     - 3.7
-    paths-ignore:
-    - 'Doc/**'
-    - 'Misc/**'
-    - '**/*.md'
-    - '**/*.rst'
   pull_request:
     branches:
     - master
     - 3.8
     - 3.7
-    paths-ignore:
-    - 'Doc/**'
-    - 'Misc/**'
-    - '**/*.md'
-    - '**/*.rst'
 
 jobs:
   build_win32: