Fix typo in automerge workflow

Description of work

This PR fixes a typo in the automerge workflow

To test:

Check that the typo has been fixed in the code. Grep for other instances of this typo

Reviewer

Please comment on the points listed below (full description). Your comments will be used as part of the gatekeeper process, so please comment clearly on what you have checked during your review. If changes are made to the PR during the review process then your final comment will be the most important for gatekeepers. In this comment you should make it clear why any earlier review is still valid, or confirm that all requested changes have been addressed.

Code Review

Is the code of an acceptable quality?
Does the code conform to the coding standards?
Are the unit tests small and test the class in isolation?
If there is GUI work does it follow the GUI standards?
If there are changes in the release notes then do they describe the changes appropriately?
Do the release notes conform to the release notes guide?

Functional Tests

Do changes function as described? Add comments below that describe the tests performed?
Do the changes handle unexpected situations, e.g. bad input?
Has the relevant (user and developer) documentation been added/updated?

Does everything look good? Mark the review as Approve. A member of @mantidproject/gatekeepers will take care of it.

Gatekeeper

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mantidproject / mantid