Fix ThreadStatus assertion crash in gtest_data_types_cache.cpp

CI: Unit tests (asan_ubsan/msan/tsan) failed with "No test result file" -
the gtest binary aborted on DataTypesCache.ReusesEntriesWithinOneQuery
with Logical error: '!current_thread', since the binary's main thread
already has a MainThreadStatus attached and ThreadStatus's constructor
asserts none is already current.

Reset current_thread before constructing the local ThreadStatus and
restore it afterward via a small RAII guard declared just before it,
matching the existing FileCacheTest fixture pattern in
src/Interpreters/tests/gtest_filecache.cpp.