update java code indentation with 2 spaces (#25122)

Author: wing328

modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/pojo.mustache

@@ -381,16 +381,16 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       {{/hasVars}}
       {{#vars}}
       {{#vendorExtensions.x-java-not-string-enum-values}}
-      if (jsonObj.get("{{{baseName}}}") != null
-              && !jsonObj.get("{{{baseName}}}").isJsonNull()
-              && jsonObj.get("{{{baseName}}}").isJsonPrimitive()
-              && jsonObj.get("{{{baseName}}}").getAsJsonPrimitive().isString()
-              && {{#lambda.javaStringLiteral}}{{{.}}}{{/lambda.javaStringLiteral}}.equals(jsonObj.get("{{{baseName}}}").getAsString())) {
-        throw new IllegalArgumentException(String.format(
-            java.util.Locale.ROOT,
-            "The field `{{{baseName}}}` in the JSON string matches a value disallowed by `not`: `%s`",
-            jsonObj.get("{{{baseName}}}").toString()));
-      }
+        if (jsonObj.get("{{{baseName}}}") != null
+                && !jsonObj.get("{{{baseName}}}").isJsonNull()
+                && jsonObj.get("{{{baseName}}}").isJsonPrimitive()
+                && jsonObj.get("{{{baseName}}}").getAsJsonPrimitive().isString()
+                && {{#lambda.javaStringLiteral}}{{{.}}}{{/lambda.javaStringLiteral}}.equals(jsonObj.get("{{{baseName}}}").getAsString())) {
+          throw new IllegalArgumentException(String.format(
+              java.util.Locale.ROOT,
+              "The field `{{{baseName}}}` in the JSON string matches a value disallowed by `not`: `%s`",
+              jsonObj.get("{{{baseName}}}").toString()));
+        }
       {{/vendorExtensions.x-java-not-string-enum-values}}
       {{#isArray}}
       {{#items.isModel}}