protobuf: add version 3.10

[stites]

Motivation for this change

Attempt to bump tensorflow-tensorboard to version 2.0

Things done

Protobuf on its own functions normally and passes its test suite. That said, I noticed that the python module fails its own test suite for any python-protobuf-3.x package. Can someone else confirm? This PR implicitly adds the protobuf 3.10 python package.

On the python side, I will note that tensorflow-tensorboard-2.0 tests pass using protobuf-3.10 -- this test suite should have heavy dependence on protobuf and might be a good proxy(?)

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc (no maintainers exist for protobuf)

[jonringer]

@GrahamcOfBorg build protobuf3_10

[jonringer]

nix-review passes on NixOS
diff LGTM
build succeeds on darwin + linux

[3 built, 1 copied (4.9 MiB), 0.6 MiB DL]
https://github.com/NixOS/nixpkgs/pull/71889
1 package were build:
protobuf3_10