Reproduction steps:
1. Create a new empty Project with an older version
2. If a Window about an available Update is not shown, Check for Updates manually
3. Skip new Version
4. Check for Updates manually

Expected result: A new available Update is shown
Actual result: The Window says that the newest version of Unity is already running

Reproducible with: 2018.4.34f1, 2019.4.27f1, 2020.3.10f1, 2021.1.9f1, 2021.2.0a18

Notes:
Cannot be tested on latest versions, as repro requires an update to be available