[aclark4life]

PYTHON-6271

Changes in this PR

Sets pymongo/_version.py to 4.21.0.dev0. This is the manual fallback for the "Set following version" step that failed in the 4.20.0 release workflow.

Test Plan

No code changes. Pre-commit hooks pass.

Checklist

Checklist for Author

• Did you update the changelog (if necessary)?
• Is the intention of the code captured in relevant tests?
• If there are new TODOs, has a related JIRA ticket been created?

Checklist for Reviewer

• Does the title of the PR reference a JIRA Ticket?
• Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
• Have you checked for spelling & grammar errors?
• Is all relevant documentation (README or docstring) updated?

[Copilot]

🟢 Approval recommended

There are no active review issues for the version bump to 4.21.0.dev0.

No open issues 🎉

What changed in this PR

Starts the next development cycle after the 4.20.0 release by manually completing the failed “Set following version” workflow step.

Changes:

• Updates the shared runtime and package version from 4.20.0 to 4.21.0.dev0.

File	Description
pymongo/​_version.py	Sets the version constant to 4.21.0.dev0.

_{Review effort: Balanced}