Update api.mustache remove nonnullable annotations in Method fetch

The current code created:
`            Method method = this.getClass().getMethod("someMethodWithHttpInfo",  @jakarta.annotation.Nonnull String.class, @jakarta.annotation.Nonnull String.class);
`
Which is invalid code. Removed the nonnull addition

Author: koosg

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

@@ -263,7 +263,7 @@ public class {{classname}} {
             ExecutableValidator executableValidator = factory.getValidator().forExecutables();
 
             Object[] parameterValues = { {{#allParams}}{{paramName}}{{^-last}}, {{/-last}}{{/allParams}} };
-            Method method = this.getClass().getMethod("{{operationId}}WithHttpInfo"{{#allParams}}, {{#isArray}}java.util.List{{/isArray}}{{#isMap}}java.util.Map{{/isMap}}{{^isArray}}{{^isMap}}{{>nullable_var_annotations}} {{{dataType}}}{{/isMap}}{{/isArray}}.class{{/allParams}});
+            Method method = this.getClass().getMethod("{{operationId}}WithHttpInfo"{{#allParams}}, {{#isArray}}java.util.List{{/isArray}}{{#isMap}}java.util.Map{{/isMap}}{{^isArray}}{{^isMap}} {{{dataType}}}{{/isMap}}{{/isArray}}.class{{/allParams}});
             Set<ConstraintViolation<{{classname}}>> violations = executableValidator.validateParameters(this, method,
                     parameterValues);