fix: remove usage of a deprecated constant. (#2138)

This change requires Jackson `2.12.0` or later.  This change is technically breaking but 5+ years old. 

FasterXML/jackson-databind@9f97baa

Fixes #2137

Author: ketan

pom.xml

@@ -89,7 +89,7 @@
       <dependency>
         <groupId>com.fasterxml.jackson</groupId>
         <artifactId>jackson-bom</artifactId>
-        <version>2.19.1</version>
+        <version>2.20.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>

src/main/java/org/kohsuke/github/GitHubClient.java

@@ -121,7 +121,7 @@ static class RetryRequestException extends IOException {
         MAPPER.setVisibility(new VisibilityChecker.Std(NONE, NONE, NONE, NONE, ANY));
         MAPPER.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
         MAPPER.configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_ENUMS, true);
-        MAPPER.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);
+        MAPPER.setPropertyNamingStrategy(PropertyNamingStrategies.SNAKE_CASE);
     }
 
     @Nonnull