Changed phase of signature step in product pom file

Attempt to address GitLab issue 3213 (https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/issues/3213)
diff --git a/releng/org.eclipse.app4mc.platform.product/pom.xml b/releng/org.eclipse.app4mc.platform.product/pom.xml
index 2dcbd59..240e08f 100644
--- a/releng/org.eclipse.app4mc.platform.product/pom.xml
+++ b/releng/org.eclipse.app4mc.platform.product/pom.xml
@@ -139,7 +139,7 @@
                 <goals>
                   <goal>sign</goal>
                 </goals>
-                <phase>package</phase>
+                <phase>prepare-package</phase>
                 <configuration>
                   <signFiles>
                     <signFile>${project.build.directory}/products/${product-uid}/win32/win32/x86_64/app4mc.exe</signFile>