Fix wrong filepaths on MVP tutorial documentation

[adriazalvarez]

Description of work

This PR adds the correct file path for the calculator example files on the recently refurbished MVP tutorial: #37953

The warnings is the following:
https://builds.mantidproject.org/job/build_and_publish_developer_site/1091/sphinx/source.cf0fecd4-b32a-475f-92f5-355421641a61/#10

Further detail of work

To test:

• No sphinx build warnings should appear on the CI.

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[robertapplin]

Thanks for fixing this, looks good to me! No documentation warnings are in the CI jobs