Fix repository name detection on AppVeyor

Author: aaubry

tools/build/BuildDefinition.cs

@@ -439,8 +439,13 @@ public static void Document(Options options)
 ");
         }
 
-        private static string GitHubRepository => Environment.GetEnvironmentVariable("GITHUB_REPOSITORY") ?? "aaubry/YamlDotNet.Sandbox";
-
+        private static string GitHubRepository =>
+            Program.Host switch
+            {
+                Host.Appveyor => Environment.GetEnvironmentVariable("APPVEYOR_REPO_NAME"),
+                _ => Environment.GetEnvironmentVariable("GITHUB_REPOSITORY")
+            }
+            ?? "aaubry/YamlDotNet.Sandbox";
 
         private static readonly Lazy<HttpClient> GitHubClient = new Lazy<HttpClient>(() =>
         {

tools/build/Program.cs

@@ -22,7 +22,7 @@ class Program
         public static bool NoPrerelease { get; private set; }
         public static string? ForcedVersion { get; private set; }
         private static bool verbose;
-        private static Host host;
+        public static Host Host { get; private set; }
         private static readonly Dictionary<Type, object> state = new Dictionary<Type, object>();
 
         private static T GetState<T>() where T : notnull
@@ -136,7 +136,7 @@ static int Main(string[] args)
 
             var (options, targets) = Options.Parse(filteredArguments);
             verbose = options.Verbose;
-            host = options.Host.DetectIfUnknown().Item1;
+            Host = options.Host.DetectIfUnknown().Item1;
 
             var operatingSystem =
                 RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
@@ -234,7 +234,7 @@ public static void WriteWarning(string text)
 
         public static void WriteImportant(string text)
         {
-            switch (host)
+            switch (Host)
             {
                 case Host.GitHubActions:
                     Console.WriteLine($"Writing a warning");