[FLINK-15268][build] Correctly set Multi-Release in manifest.

FLINK-14905 introduced a multi-release approach to bundle libraries
for different JDK versions. However, the multi-release flag was not
correctly set, which effectively disabled the mechanism and lead to
incomplete dependencies on Java 11. This commit fixes the setup, such
that the Java 11 libraries are correctly loaded.

flink-dist/pom.xml

@@ -573,16 +573,16 @@ under the License.
 						<goals>
 							<goal>jar</goal>
 						</goals>
-						<configuration>
-							<archive>
-								<manifestEntries>
-									<!-- jaxb-api is packaged as an optional dependency that is only accessible on Java 11 -->
-									<Multi-Release>true</Multi-Release>
-								</manifestEntries>
-							</archive>
-						</configuration>
 					</execution>
 				</executions>
+				<configuration>
+					<archive>
+						<manifestEntries>
+							<!-- jaxb-api is packaged as an optional dependency that is only accessible on Java 11 -->
+							<Multi-Release>true</Multi-Release>
+						</manifestEntries>
+					</archive>
+				</configuration>
 			</plugin>
 
 			<plugin>