Don't run doc tests if only dev docs have changed

[jhaigh0]

Description of work

Fixes #37147

To test:

• Made this pr from a branch based on this one. If you look at the output of the docs job you can see it hasn't run the doc tests: Don't merge. Test pr for conda build script change #37361
• This pr (also branching from and back into this branch) has a change to the user docs, so should run the doc tests as normal Don't merge, second doc changes test pr #37362

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[robertapplin]

I can confirm that the doc tests are not run if a change has only been made to the dev-docs. The doc tests are run as expected when a change is made to the normal docs