Fix names parsed from build.json

Robust.Server/ServerStatus/StatusHost.cs

@@ -172,8 +172,8 @@ namespace Robust.Server.ServerStatus
         private sealed class BuildInfo
         {
             [JsonProperty("engine_version")] public string EngineVersion = default!;
-            [JsonProperty("hashes")] public string? Hash;
-            [JsonProperty("downloads")] public string Download = default!;
+            [JsonProperty("hash")] public string? Hash;
+            [JsonProperty("download")] public string Download = default!;
             [JsonProperty("fork_id")] public string ForkId = default!;
             [JsonProperty("version")] public string Version = default!;
         }

Robust.Shared/Serialization/RobustMappedStringSerializer.cs

@@ -480,7 +480,7 @@ namespace Robust.Shared.Serialization
             var hashStr = Convert.ToBase64String(MappedStringsHash);
             hashStr = ConvertToBase64Url(hashStr);
 
-            var fileName = CacheForHash(hashStr);
+            var fileName = CacheForHash(hashStr)!;
             using var file = File.OpenWrite(fileName);
             stream.CopyTo(file);