find_template_parameters needs to find the mention of T in the lambda.
Fixing that leaves this as a hard error, which may be surprising but is
consistent with lambdas in other SFINAE contexts like template argument
deduction.

gcc/cp/ChangeLog
2020-02-15  Jason Merrill  <jason@redhat.com>

	PR c++/92556
	* pt.c (any_template_parm_r): Look into lambda body.