Set write permissions for contents and pull-requests for dispatch events

[weiji14]

Description of proposed changes

The /format comment triggered at #4134 (comment) did not work, failing at https://github.com/GenericMappingTools/pygmt/actions/runs/18181218096/job/51757194575#step:2:17 with:

Warning: Failed to set reaction on comment ID 3358748228.
Command 'format' to be dispatched.
Error: Resource not accessible by integration

Specifically, no emoji reactions were created, and the dispatch event did not happen.

Need to set the following permissions:

• contents: write to execute repo dispatch event and for git to push
• pull-requests: write for peter-evans/slash-command-dispatch to create PR reaction

Based on similar PRs I did recently at pangeo-data/pangeo-docker-images#626 and pangeo-data/pangeo-docker-images#625

References:

• "Warning: Failed to set reaction on comment ID xx." peter-evans/slash-command-dispatch#376
• Error: Resource not accessible by integration peter-evans/repository-dispatch#196 (comment)

Addresses #3874 (comment)

Preview:

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash command is:

• /format: automatically format and lint the code

[weiji14]

Ok, dispatch worked (there are emojis on #4134 (comment)), but the format command failed at https://github.com/GenericMappingTools/pygmt/actions/runs/18182144257/job/51759958626#step:6:33 with fatal: could not read Username for 'https://github.com/': No such device or address 😅 Think we need to set persist-credentials: true too.