Update Mapper4 SetBadMetadata VTS test for optional metadata

The common decode function for optional gralloc4 metadata
`android::gralloc4::decodeOptionalMetadata()` treats an empty
input `hidl_vec<uint8_t>` as `std::nullopt` and not a bad
value. aosp/1907915 previously tried to update the encoding
and decoding of optional metadata in order to distinguish
this case but the change broke GRF. Instead, let's update the
SetBadMetadata test to use some actual incorrect data for the
optional metadata tests instead of an empty vec.

Bug: b/207388558
Test: cvd start
Test: VtsHalGraphicsMapperV4_0TargetTest
Change-Id: I87c20930cb701e87c89489bd0359cce0522cfe44