Update CHANGELOG.md

Author: rly

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Enhancements and minor changes
 - Add `NWBHDF5IO.can_read()`. @bendichter [#1703](https://github.com/NeurodataWithoutBorders/pynwb/pull/1703)
 - Add `pynwb.get_nwbfile_version()`. @bendichter [#1703](https://github.com/NeurodataWithoutBorders/pynwb/pull/1703)
+- Fix usage of the `validate` function in the `pynwb.testing.testh5io` classes and cache the spec by default in those classes. @rly [#1782](https://github.com/NeurodataWithoutBorders/pynwb/pull/1782)
 
 ## PyNWB 2.5.0 (August 18, 2023)