deps(pandas-gbq): drop Python 3.9

[tswast]

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Fixes internal b/490130968 🦕

[gemini-code-assist]

Code Review

This pull request updates the minimum supported Python version from 3.9 to 3.10 and increases the minimum version requirements for several core dependencies, including numpy, pandas, pyarrow, geopandas, and Shapely. Additionally, it replaces the Python 3.9 testing constraints file with a new version for Python 3.10 to reflect these updated lower bounds. I have no feedback to provide.

[tswast]

Oh, I see that 3.9 tests are still present. Perhaps this needs to change repo-wide?