Release 3.6.6 (2025-06-17)

What's Changed

Release v3.6.4 by @github-actions in DeterminateSystems/nix-src#109
Fixup the complainy docs line by @grahamc in DeterminateSystems/nix-src#111
Move the actual vm tests / flake regressions into the generic build phase by @grahamc in DeterminateSystems/nix-src#112
Fix broken fetchToStore() caching by @edolstra in DeterminateSystems/nix-src#110
Parallelize the flake regression suite by @grahamc in DeterminateSystems/nix-src#114
Don't build fallback-paths if we didn't build aarch64-linux and x86 d… …arwin by @grahamc in DeterminateSystems/nix-src#116
Use GHA runners for VMs since they have KVM by @grahamc in DeterminateSystems/nix-src#118
fetchToStore() cache: Use content hashes instead of store paths by @edolstra in DeterminateSystems/nix-src#115
Release v3.6.5 by @github-actions in DeterminateSystems/nix-src#119

Full Changelog: v3.6.3...v3.6.6