Add targeting criteria to avoid the MR experiments on desktop

[shell1]

For the new waldo experiments - they will want to avoid the MRs on desktop - https://docs.google.com/document/d/16X9l9TE7VX6hJPfqqZ9r41YjmShHjrY4CavEJcZ_pyU/edit#heading=h.4sp6t4yuhnu2

So the advanced targeting criteria needed is avoid: https://experimenter.services.mozilla.com/nimbus/106-major-release-firefox-existing-user-experience https://experimenter.services.mozilla.com/nimbus/106-major-release-firefox-new-user

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