[ci] Chore: Remove SSH_KEY secret

[etrepum]

Description

Committing to the repo doesn't need an SSH_KEY secret because the GITHUB_TOKEN can do it all in safer manner.

Test plan

• Use the updated workflow to create a release branch
  • ✅ https://github.com/facebook/lexical/actions/runs/13185564867/job/36806710812
• The workflow should create the release branch correctly
  • ✅ https://github.com/facebook/lexical/tree/latest__release
  • ✅ https://github.com/facebook/lexical/tree/0.24.0__release
• The tests should run after creating a PR with the branch
  • IIRC there are some limitations in the GitHub APIs to prevent workflows from infinitely triggering other workflows, but I think since a human manually creates the release PR this might not be an issue for us. Be careful to verify this.
  • ✅ [DO NOT MERGE] Test release PR for #7143 #7144

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Name	Status	Preview	Comments	Updated (UTC)
lexical	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 6, 2025 6:34pm
lexical-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 6, 2025 6:34pm