added PR reference

Author: jonas-hurst

CHANGELOG.md

@@ -14,7 +14,7 @@
 - Type of `proj:code` setter ([#1560](https://github.com/stac-utils/pystac/pull/1560))
 - Use `urllib3` to fix parsing non-ascii in urls ([#1566](https://github.com/stac-utils/pystac/pull/1566))
 - Some return types and other **mypy** nits ([#1569](https://github.com/stac-utils/pystac/pull/1569))
-- `extensions.mlm` various fixes
+- `extensions.mlm` various fixes ([#1571](https://github.com/stac-utils/pystac/pull/1571))
   - Fixed ResizeType typos `interpolation-nearest` and `interpolation-linear` 
   - Fixed displaying the correct property in error message for `ResultStructure.data_type` 
   - Fixed `ValueScaling.maximum` setter to pop when None is given