system.text.json: update github rest api

Update GitHub REST API-related code to use System.Text.Json rather than
Json.NET for JSON deserialization.

Author: ldennington

src/shared/GitHub/GitHubRestApi.cs

@@ -8,7 +8,8 @@
 using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using GitCredentialManager;
-using Newtonsoft.Json;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 
 namespace GitHub
 {
@@ -105,7 +106,7 @@ public async Task<GitHubUserInfo> GetUserInfoAsync(Uri targetUri, string accessT
 
                     string json = await response.Content.ReadAsStringAsync();
 
-                    return JsonConvert.DeserializeObject<GitHubUserInfo>(json);
+                    return JsonSerializer.Deserialize<GitHubUserInfo>(json);
                 }
             }
         }
@@ -124,7 +125,7 @@ public async Task<GitHubMetaInfo> GetMetaInfoAsync(Uri targetUri)
 
                 string json = await response.Content.ReadAsStringAsync();
 
-                return JsonConvert.DeserializeObject<GitHubMetaInfo>(json);
+                return JsonSerializer.Deserialize<GitHubMetaInfo>(json);
             }
         }
 
@@ -265,16 +266,16 @@ public void Dispose()
 
     public class GitHubUserInfo
     {
-        [JsonProperty("login")]
+        [JsonPropertyName("login")]
         public string Login { get; set; }
     }
 
     public class GitHubMetaInfo
     {
-        [JsonProperty("installed_version")]
+        [JsonPropertyName("installed_version")]
         public string InstalledVersion { get; set; }
 
-        [JsonProperty("verifiable_password_authentication")]
+        [JsonPropertyName("verifiable_password_authentication")]
         public bool VerifiablePasswordAuthentication { get; set; }
     }