Revert "Bump maven-shared-resources from 2 to 4 (#31)"

This reverts commit be57b24.

As maven-shared-resources 3+ has this commit:
apache/maven-shared-resources@5fbc3eb

That according to doco
https://checkstyle.sourceforge.io/config_filefilters.html#BeforeExecutionExclusionFileFilter
is "since 7.2", while maven-checkstyle-plugin:3.0.0 uses checkstyle 6.18

Moreover, maven-shared-resources 4+ has this commit:
apache/maven-shared-resources@fbef6f6
that requires checkstyle 8.42+

Currently there is no release of maven-checkstyle-plugin that uses checkstyle 8.42+
hence reverting this commit.

maven-extensions/pom.xml

@@ -79,7 +79,7 @@ under the License.
             <dependency>
               <groupId>org.apache.maven.shared</groupId>
               <artifactId>maven-shared-resources</artifactId>
-              <version>4</version>
+              <version>2</version>
             </dependency>
           </dependencies>
         </plugin>

maven-plugins/pom.xml

@@ -92,7 +92,7 @@ under the License.
             <dependency>
               <groupId>org.apache.maven.shared</groupId>
               <artifactId>maven-shared-resources</artifactId>
-              <version>4</version>
+              <version>2</version>
             </dependency>
           </dependencies>
         </plugin>

maven-shared-components/pom.xml

@@ -89,7 +89,7 @@ under the License.
             <dependency>
               <groupId>org.apache.maven.shared</groupId>
               <artifactId>maven-shared-resources</artifactId>
-              <version>4</version>
+              <version>2</version>
             </dependency>
           </dependencies>
         </plugin>

pom.xml

@@ -1027,7 +1027,7 @@ under the License.
             <dependency>
               <groupId>org.apache.maven.shared</groupId>
               <artifactId>maven-shared-resources</artifactId>
-              <version>4</version>
+              <version>2</version>
             </dependency>
           </dependencies>
         </plugin>