Unity detected a security issue in all versions of the Unity editor, so they released new versions of all historical builds and asked developers to re-build their games on the new version, so this is just that.
Patch 1.7.5 -- Just updating Unity version
Source: Steam Community (opens in a new tab)
Build and release context
Steam update times within 24 hours of this post. Matching dates do not confirm which build it describes.
Build 20280984 · public branch
Steam updated · First observed