twister: tests: Add test verifying integration mode / integration_platforms

[PerMac]

Is your enhancement proposal related to a problem? Please describe.
The integration mode / integration_platforms list can stop operating as it should. It already happened here #32835. This can cause severe problems: the faulty code can get merged into the main due to CI not verifying it in the proper scope (already seen due to the linked issue).

Describe the solution you'd like
A test(s) verifying the correctness of integration mode should be added. The test(s) should call twister with -G argument for a sample containing both default and non-default platforms in its integration_platforms list. It should be verified then the sample was built/executed on all the platforms from the integration_platforms list.