Add changenote.+ fix typo

Author: joefarebrother

python/ql/src/Functions/SignatureOverriddenMethod.qhelp

@@ -7,7 +7,7 @@
 <overview>
 <p> When the signature of a method of a base class and a method of a subclass that overrides it don't match, a call to the base class method 
 may not be a valid call to the subclass method, and thus raise an exception if an instance of the subclass is passed instead. 
-If following the Liskov Substitution Principle, in which an instance of a subclass should be usable in every context as though it were a an 
+If following the Liskov Substitution Principle, in which an instance of a subclass should be usable in every context as though it were an 
 instance of the base class, this behavior breaks the principle.
 </p>
 

python/ql/src/change-notes/2025-08-19-signature-mismatch.md

@@ -0,0 +1,5 @@
+---
+category: minorAnalysis
+---
+* The `py/inheritance/signature-mismatch` query has been modernized. It produces more precise results and more descriptive alert messages. 
+* The `py/inheritance/incorrect-overriding-signature` query has been deprecated. Its results have been consolidated into the `py/inheritance/signature-mismatch` query.