libstdc++: Increase timeouts for PSTL tests in debug mode [PR90276]

libstdc++: Increase timeouts for PSTL tests in debug mode [PR90276]

These tests compile very slowly in debug mode.

libstdc++-v3/ChangeLog:

	PR libstdc++/90276
	* testsuite/25_algorithms/pstl/alg_modifying_operations/rotate_copy.cc:
	Increase timeout for debug mode.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/transform_binary.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/mismatch.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/lexicographical_compare.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/minmax_element.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/set_symmetric_difference.cc:
	Likewise.