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
to fix the grammar.
diff --git a/Doc/library/chunk.rst b/Doc/library/chunk.rst
index 04c7e27..d31fa0a 100644
--- a/Doc/library/chunk.rst
+++ b/Doc/library/chunk.rst
@@ -48,7 +48,7 @@
the :class:`Chunk` class defined here is to instantiate an instance at the start
of each chunk and read from the instance until it reaches the end, after which a
new instance can be instantiated. At the end of the file, creating a new
-instance will fail with a :exc:`EOFError` exception.
+instance will fail with an :exc:`EOFError` exception.
.. class:: Chunk(file[, align, bigendian, inclheader])