Update changelog for azure-identity 1.6.0b3
# Release History
-## 1.6.0b3 (Unreleased)
+## 1.6.0b3 (2021-04-06)
### Breaking Changes
> These changes do not impact the API of stable versions such as 1.5.0.
> Only code written against a beta version such as 1.6.0b1 may be affected.
