These will never suceed while running the tests in the Nix sandbox, and
skipping them leads to very noticable (~51%) speedups.
Before:
```
Benchmark 1: nix build .#hydraJobs.x86_64-linux.external-unstable --rebuild
Time (mean ± σ): 151.737 s ± 1.074 s [User: 0.310 s, System: 0.289 s]
Range (min … max): 150.321 s … 153.512 s 10 runs
```
After:
```
Benchmark 1: nix build .#hydraJobs.x86_64-linux.external-unstable --rebuild
Time (mean ± σ): 74.010 s ± 0.746 s [User: 0.269 s, System: 0.266 s]
Range (min … max): 72.814 s … 75.190 s 10 runs
```
0774c93ae6