CI: Don't run cron for forks

[hugovk]

• [n/a] closes #xxxx (Replace xxxx with the GitHub issue number)
• [n/a] Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• [n/a] Added type annotations to new arguments/methods/functions.
• [n/a?] Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

The codeql and stale-pr workflows run on a cron:

on:
  schedule:
    # every day at midnight
    - cron: "0 0 * * *"

As does the wheels workflow:

on:
  schedule:
  #        ┌───────────── minute (0 - 59)
  #        │  ┌───────────── hour (0 - 23)
  #        │  │ ┌───────────── day of the month (1 - 31)
  #        │  │ │ ┌───────────── month (1 - 12 or JAN-DEC)
  #        │  │ │ │ ┌───────────── day of the week (0 - 6 or SUN-SAT)
  #        │  │ │ │ │
  - cron: "27 3 */1 * *"

These are useful for the upstream https://github.com/pandas-dev/pandas repo but unnecessary for contributors' forks:

They also trigger emails when they fail on the fork:

Similar to autoupdate-pre-commit-config, let's only run the schedule for upstream:

pandas/.github/workflows/autoupdate-pre-commit-config.yml

Line 16 in 956b800

if: github.repository_owner == 'pandas-dev'

[mroeschke]

Makes sense. Thanks @hugovk