Bump sphinx-maven-plugin from 2.3.1 to 2.4.0

Bumps [sphinx-maven-plugin](https://github.com/trustin/sphinx-maven-plugin) from 2.3.1 to 2.4.0.
- [Release notes](https://github.com/trustin/sphinx-maven-plugin/releases)
- [Commits](trustin/sphinx-maven-plugin@sphinx-maven-plugin-2.3.1...sphinx-maven-plugin-2.4.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

pom.xml

@@ -578,7 +578,7 @@
                 <plugin>
                     <groupId>kr.motd.maven</groupId>
                     <artifactId>sphinx-maven-plugin</artifactId>
-                    <version>2.3.1</version>
+                    <version>2.4.0</version>
                 </plugin>
                 <plugin>
                     <groupId>org.simplify4u.plugins</groupId>