Bump github.com/google/flatbuffers

[pjbgf]

Flatbuffers is an indirect dependency (via github.com/dgraph-io/badger/v3) which is impacted by 13 security advisories recently discovered.
An official fix has not yet been released and vulnerabilities scanners such as trivy do not pick it up. This issue is to keep track of the issue an patch it in a timely manner.

Security Advisories:
OSV-2021-1229: Heap-buffer-overflow in flatbuffers::JsonPrinter::GenFieldOffset
OSV-2021-1249: Heap-buffer-overflow in int flatbuffers::ReadScalar<int>
OSV-2021-1314: Use-of-uninitialized-value in LoadBinarySchema
OSV-2021-1678: Heap-buffer-overflow in flatbuffers::EscapeString
OSV-2021-1695: Heap-buffer-overflow in flexbuffers::Verifier::VerifyRef
OSV-2021-281: Heap-buffer-overflow in flatbuffers::Table* flatbuffers::GetMutableRoot<flatbuffers::Table>
OSV-2021-308: Heap-buffer-overflow in flatbuffers::JsonPrinter::GenFieldOffset
OSV-2021-333: Heap-buffer-overflow in int flatbuffers::ReadScalar<int>
OSV-2021-347: Heap-buffer-overflow in flatbuffers::Table* flatbuffers::GetMutableRoot<flatbuffers::Table>
OSV-2021-349: Heap-buffer-overflow in flatbuffers::vector_downward::fill
OSV-2021-520: Heap-buffer-overflow in flatbuffers::EscapeString
OSV-2021-541: Heap-buffer-overflow in flatbuffers::Table* flatbuffers::GetMutableRoot<flatbuffers::Table>
OSV-2021-581: UNKNOWN READ in unsigned short flatbuffers::ReadScalar<unsigned short>

[pjbgf]

The majority of the issues are already patched at the project's master branch. A release should soon follow.