doc: add issue number to changelog entry of pr#2148

Author: sebix

CHANGELOG.md

@@ -94,7 +94,7 @@ CHANGELOG
   - Decorator `skip_ci` also detects `dpkg-buildpackage` environments by checking the environment variable `DEB_BUILD_ARCH` (PR#2123 by Sebastian Wagner).
 - Also test on Python 3.10 (PR#2140 by Sebastian Wagner).
 - Switch from nosetests to pytest, as the former does not support Python 3.10 (PR#2140 by Sebastian Wagner).
-- CodeQL Github Actions `exponential backtracking on strings` fixed. (PR#2148 by Sebastian Waldbauer)
+- CodeQL Github Actions `exponential backtracking on strings` fixed. (PR#2148 by Sebastian Waldbauer, fixes #2138)
 
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