Issue #25523: Correct "a" article to "an" article
This changes the main documentation, doc strings, source code comments, and a
couple error messages in the test suite. In some cases the word was removed
or edited some other way to fix the grammar.
diff --git a/Doc/library/pyexpat.rst b/Doc/library/pyexpat.rst
index 78aa99c..620ffb1 100644
--- a/Doc/library/pyexpat.rst
+++ b/Doc/library/pyexpat.rst
@@ -763,7 +763,7 @@
.. data:: XML_ERROR_UNDEFINED_ENTITY
- A reference was made to a entity which was not defined.
+ A reference was made to an entity which was not defined.
.. data:: XML_ERROR_UNKNOWN_ENCODING