Fix Azure Pipelines change detection. (#72824)

changelogs/fragments/ansible-test-azp-change-detection.yml

@@ -0,0 +1,2 @@
+bugfixes:
+    - ansible-test - Correctly detect changes in a GitHub pull request when running on Azure Pipelines.

test/lib/ansible_test/_internal/ci/azp.py

@@ -208,10 +208,10 @@ class AzurePipelinesChanges:
         if self.base_commit:
             self.base_commit = self.git.run_git(['rev-parse', self.base_commit]).strip()
 
-            # <rev1>...<rev2>
-            # Include commits that are reachable from <rev2> but exclude those that are reachable from <rev1>.
-            # see: https://git-scm.com/docs/gitrevisions
-            dot_range = '%s..%s' % (self.base_commit, self.commit)
+            # <commit>...<commit>
+            # This form is to view the changes on the branch containing and up to the second <commit>, starting at a common ancestor of both <commit>.
+            # see: https://git-scm.com/docs/git-diff
+            dot_range = '%s...%s' % (self.base_commit, self.commit)
 
             self.paths = sorted(self.git.get_diff_names([dot_range]))
             self.diff = self.git.get_diff([dot_range])