Add example test for forwards compat of custom setting #302

Job	Run time
Setup and Cache Dependencies	1m 43s
Conan (unittests) (3.8)	1m 14s
Conan (integration) (3.8)	4m 36s
Conan (functional) (3.8)	22m 53s
Conan (unittests) (3.12)	43s
Conan (integration) (3.12)	1m 48s
Conan (functional) (3.12)	21m 48s
Conan (unittests) (3.13)	42s
Conan (integration) (3.13)	3m 10s
Conan (functional) (3.13)	26m 0s
	1h 24m 37s

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