Drop support for Python 3.9

[QMalcolm]

Housekeeping

• I am a maintainer of dbt-core

Short description

Python 3.9 went EOL this month (Oct 2025). As such, we should drop support for it in all future release (dbt-core 1.11.0+)

Acceptance criteria

Require python >= 3.10

Suggested Tests

Remove 3.9 from testing matrix

Impact to Other Teams

N/A

Will backports be required?

No, it's forward facing only

Context

No response

[FishtownBuildBot]

Opened a new issue in dbt-labs/docs.getdbt.com: dbt-labs/docs.getdbt.com#8107