CI: Validate on InfluxDB 3.9

[amotl]

Just probing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.19%. Comparing base (a386d10) to head (7bcffc3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #244   +/-   ##
=======================================
  Coverage   84.19%   84.19%           
=======================================
  Files          12       12           
  Lines         715      715           
=======================================
  Hits          602      602           
  Misses        113      113           

Flag	Coverage Δ
unittests	84.19% <ø> (ø)

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