Revert "Disable BitStructs::NestedFieldAssignment."

This reverts commit 8404f348c96c929981b157b8240d55bc81222003.

Reason for revert: b/148125232 was fixed
Bug: 148125232

Change-Id: I5a8232959f804c203850aaaf3dac97e286dd188f
diff --git a/libartbase/base/bit_struct_test.cc b/libartbase/base/bit_struct_test.cc
index 6b0d0f0..2055782 100644
--- a/libartbase/base/bit_struct_test.cc
+++ b/libartbase/base/bit_struct_test.cc
@@ -297,7 +297,7 @@
   BITSTRUCT_UINT(/*lsb=*/0, /*width=*/ 2 * MixedSizeBitStruct::BitStructSizeOf()) alias_all;
 BITSTRUCT_DEFINE_END(NestedStruct);
 
-TEST(BitStructs, DISABLED_NestedFieldAssignment) {
+TEST(BitStructs, NestedFieldAssignment) {
   MixedSizeBitStruct mixed_all_1s{};
   mixed_all_1s.alias_all = 0xFFFFFFFFu;