serializers: DataCite to DCAT-AP: fix missing prov namespace for contributors project roles

[ptamarit]

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Fixes https://github.com/zenodo/ops/issues/356

Description

How to reproduce the problem:

• Create a record with a contributor having one of the roles: Project Leader, Project Manager, Project Member
• Try to export the report to DCAT
• You will get the error XSLTApplyError: Undefined variable in invenio_rdm_records/resources/serializers/dcat/__init__.py

This pull request fixes this bug.

FYI, I created a pull request upstream with the same fix: https://github.com/ec-jrc/datacite-to-dcat-ap/pull/8

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• [x] I'm aware of the code of conduct.
• [x] I've created logical separate commits and followed the commit message format.
• [x] I've added relevant test cases.
• [x] I've added relevant documentation.
• [x] I've marked translation strings (for relevant code).
• [x] I've followed the CSS/JS and React guidelines (for relevant code).
• [x] I've followed the web accessibility guidelines (for relevant code).
• [x] I've followed the user interface guidelines (for relevant code).
• [x] I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• [ ] I've NOT included third-party code (copy/pasted source code or new dependencies). -> I did copy the code from https://github.com/ec-jrc/datacite-to-dcat-ap/blob/master/datacite-to-dcat-ap.xsl

Third-party code

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