Faster `dotnet restore` for backend container #456

All 30 tests pass in 12s

30 tests +4 30 ✔️ +4 12s ⏱️ - 10m 2s
  6 suites ±0   0 💤 ±0
  1 files ±0   0 ❌ ±0

Results for commit 75f0612. ± Comparison against earlier commit 5fad5d8.