Python: Add change-note about UntrustedStringKind imports

Author: RasmusWL

change-notes/1.25/analysis-python.md

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+# Improvements to Python analysis
+
+The following changes in version 1.25 affect Python analysis in all applications.
+
+## General improvements
+
+
+## New queries
+
+| **Query**                   | **Tags**  | **Purpose**                                                        |
+|-----------------------------|-----------|--------------------------------------------------------------------|
+
+
+## Changes to existing queries
+
+| **Query**                  | **Expected impact**    | **Change**                                                       |
+|----------------------------|------------------------|------------------------------------------------------------------|
+
+
+## Changes to libraries
+
+* Importing `semmle.python.web.HttpRequest` will no longer import `UntrustedStringKind` transitively. `UntrustedStringKind` is the most commonly used non-abstract subclass of `ExternalStringKind`. If not imported (by one mean or another), taint-tracking queries that concern `ExternalStringKind` will not produce any results. Please ensure such queries contain an explicit import (`import semmle.python.security.strings.Untrusted`).