chore: Update CLA link

[Prusdrum]

Description

We had to update the link after migrating the CLA tool: https://simpleclub.slack.com/archives/CATPELDMH/p1736153833672199?thread_ts=1733313483.185789&cid=CATPELDMH

Related issues & PRs

SC-14984

Checklist

Remove If [...] items that do not apply to your PR.

• I have made myself familiar with the CaTeX
  contributing guide.
• I added a PR description.
• I linked all related issues and PRs I could find (no links if there are none).
• If this PR changes anything about the main math_keyboard or example package
  (also README etc.), I created an entry in CHANGELOG.md (## UPCOMING RELEASE if the change
  on its own is not worth an update).
• If this PR includes a notable change in the math_keyboard package, I updated the version
  according to Dart's semantic versioning.
• If there is new functionality in code, I added tests covering all my additions.
• All required checks pass.

[CLAassistant]

All committers have signed the CLA.