chore: update pygithub version

[rexledesma]

Summary

Update the PyGithub dependency so uv sync works out of the box.

Test Plan

Before:

❯ uv sync
Using CPython 3.13.3
Creating virtual environment at: .venv
  × No solution found when resolving dependencies:
  ╰─▶ Because sqlmesh[github] depends on pygithub>=2.5.0,<2.6.dev0 and sqlmesh[dev] depends on pygithub>=2.6.0, we can conclude that sqlmesh[dev] and
      sqlmesh[github] are incompatible.
      And because your project requires sqlmesh[dev] and sqlmesh[github], we can conclude that your project's requirements are unsatisfiable.

After:

❯ uv sync
Resolved 330 packages in 1.54s
      Built sqlmesh @ file:///Users/rexledesma/Documents/projects/sqlmesh

[CLAassistant]

All committers have signed the CLA.

[erindru]

Huh, this is aptly timed, I just noticed this today as well. Thanks!