Update to Nix master

The point of this branch is to always track Nix master, so we are
proactively ready to upgrade to the next Nix release when it is ready.

Flake lock file updates:

• Updated input 'nix':
    'github:NixOS/nix/50f8f1c8bc019a4c0fd098b9ac674b94cfc6af0d' (2023-11-27)
  → 'github:NixOS/nix/c3827ff6348a4d5199eaddf8dbc2ca2e2ef46ec5' (2023-12-07)
• Added input 'nix/libgit2':
    'github:libgit2/libgit2/45fd9ed7ae1a9b74b957ef4f337bc3c8b3df01b5' (2023-10-18)

flake.nix

@@ -2,7 +2,7 @@
   description = "A Nix-based continuous build system";
 
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.05";
-  inputs.nix.url = "github:NixOS/nix/2.19.2";
+  inputs.nix.url = "github:NixOS/nix";
   inputs.nix.inputs.nixpkgs.follows = "nixpkgs";
 
   outputs = { self, nixpkgs, nix }:

src/hydra-queue-runner/build-remote.cc

@@ -350,7 +350,7 @@ static std::map<StorePath, ValidPathInfo> queryPathInfos(
         auto references = ServeProto::Serialise<StorePathSet>::read(localStore, conn);
         readLongLong(conn.from); // download size
         auto narSize = readLongLong(conn.from);
-        auto narHash = Hash::parseAny(readString(conn.from), htSHA256);
+        auto narHash = Hash::parseAny(readString(conn.from), HashAlgorithm::SHA256);
         auto ca = ContentAddress::parseOpt(readString(conn.from));
         readStrings<StringSet>(conn.from); // sigs
         ValidPathInfo info(localStore.parseStorePath(storePathS), narHash);

src/hydra-queue-runner/nar-extractor.cc

@@ -42,7 +42,7 @@ struct Extractor : ParseSink
     void preallocateContents(uint64_t size) override
     {
         expectedSize = size;
-        hashSink = std::make_unique<HashSink>(htSHA256);
+        hashSink = std::make_unique<HashSink>(HashAlgorithm::SHA256);
     }
 
     void receiveContents(std::string_view data) override

src/hydra-queue-runner/queue-monitor.cc

@@ -677,7 +677,7 @@ BuildOutput State::getBuildOutputCached(Connection & conn, nix::ref<nix::Store>
                 product.fileSize = row[2].as<off_t>();
             }
             if (!row[3].is_null())
-                product.sha256hash = Hash::parseAny(row[3].as<std::string>(), htSHA256);
+                product.sha256hash = Hash::parseAny(row[3].as<std::string>(), HashAlgorithm::SHA256);
             if (!row[4].is_null())
                 product.path = row[4].as<std::string>();
             product.name = row[5].as<std::string>();