tweak TEST_MAPPING for libcore.content.type

CL https://r.android.com/1133257 forgot to add the corresponding
CtsLibcoreTestCases test package to presubmit. This CL adds it.

Test: croot libcore/luni/src/main/java/libcore/content/type && atest
Change-Id: I63e35d492a577775ac0eafd986d91a4eefc11972
1 file changed