PYTHON-4883 Add release date to changelog entries

- No changes in 4.0.1 or 4.0.2

Author: aclark4life

doc/changelog.rst

@@ -797,9 +797,13 @@ in this release.
 Changes in Version 4.0.2 (2022/03/03)
 -------------------------------------
 
+- No changes
+
 Changes in Version 4.0.1 (2021/12/07)
 -------------------------------------
 
+- No changes
+
 Changes in Version 4.0 (2021/11/29)
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