Refine tag regex to deal with {@code ...} text

Update `AT_TAG_PATTERN` regex in `SpringJavadocCheck` so that
text with `{@code ...}` escapes aren't considered.

Fixes gh-291

spring-javaformat/spring-javaformat-checkstyle/src/main/java/io/spring/javaformat/checkstyle/check/SpringJavadocCheck.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2020 the original author or authors.
+ * Copyright 2017-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -56,7 +56,7 @@ public class SpringJavadocCheck extends AbstractSpringCheck {
 
 	private static final Pattern SINCE_TAG_PATTERN = Pattern.compile("@since\\s+(.*)");
 
-	private static final Pattern AT_TAG_PATTERN = Pattern.compile("@\\w+\\s+.*");
+	private static final Pattern AT_TAG_PATTERN = Pattern.compile("[^{]@\\w+\\s+.*");
 
 	private static final Pattern NON_JAVADOC_COMMENT = Pattern.compile("\\(non-Javadoc\\)", Pattern.CASE_INSENSITIVE);
 

spring-javaformat/spring-javaformat-checkstyle/src/test/resources/check/JavadocMethodEmptyLineBeforeTagWithStarAtEnd.txt

@@ -0,0 +1 @@
++0 errors

spring-javaformat/spring-javaformat-checkstyle/src/test/resources/source/JavadocMethodEmptyLineBeforeTagWithStarAtEnd.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2017-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Javadoc with white space.
+ * @param <T> this is a valid param
+ * @author Sushant Kumar Singh
+ */
+public class JavadocMethodEmptyLineBeforeTagWithStarAtEnd<T> {
+
+	/**
+	 * First paragraph.
+	 *
+	 * <p>Second paragraph contains an asterisk in a code element: {@code *}.
+	 * @since 1.0
+	 */
+	public void test() {
+	}
+
+}