Update dependency org.codehaus.mojo:flatten-maven-plugin to v1.7.3

Author: renovate[bot]

pom.xml

@@ -202,7 +202,7 @@
             <plugin>
                 <groupId>org.codehaus.mojo</groupId>
                 <artifactId>flatten-maven-plugin</artifactId>
-                <version>1.2.7</version>
+                <version>1.7.3</version>
                 <executions>
                     <execution>
                         <id>flatten</id>