gh-150771: Fix NEWS entry doc references for docs CI

Use plain backticks for set_content() instead of a broken :func: target.

Author: bhuvi27

Misc/NEWS.d/next/Library/2026-06-09-12-00-00.gh-issue-150771.K7mNx2.rst

@@ -1,4 +1,4 @@
 Fix :mod:`email` messages created with ``shift_jis`` or ``euc-jp`` charsets.
-:func:`email.contentmanager.set_text_content` now stores the payload using
-the output charset (``iso-2022-jp``) so :func:`str` on the message no longer
-raises :exc:`UnicodeEncodeError`.
+``set_content()`` now stores the payload using the output charset
+(``iso-2022-jp``) so printing the message no longer raises
+:exc:`UnicodeEncodeError`.