Prevent readability from running on Dependabot PRs

### TL;DR

PRs like https://github.com/abcxyz/github-action-dispatcher/pull/64 will be blocked on merge because dependabot does not have access to secrets.

### Expected behavior

_No response_

### Observed behavior

_No response_

### Environment Details

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### Additional information

_No response_

Look at the repository's workflows to find where the 'readability' check runs. Examine the linked PR #64 in the abcxyz/github-action-dispatcher repository to understand the failure context. Modify the workflow to skip the readability check for PRs authored by dependabot. Test by creating a dummy PR or checking workflow syntax.

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