Added changelog entry.

Author: manugv

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - `openeo.testing.io.TestDataLoader`: unit test utility to compactly load (and optionally preprocess) tests data (text/JSON/...)
 - `openeo.Connection`: automatically retry API requests on `429 Too Many Requests` HTTP errors, with appropriate delay if possible ([#441](https://github.com/Open-EO/openeo-python-client/issues/441))
+- Introduced the `pixel_tolerance` variable in `openeo.testing.results` to specify the allowable percentage of differing pixels in the results.
 
 ### Changed