Fix bad casting causing all entries to be unknown

Author: kysmith-csg

org.eclipse.m2e.core.ui/src/org/eclipse/m2e/core/ui/internal/preferences/LifecycleMappingsViewer.java

@@ -444,7 +444,8 @@ String getSourcelabel(MojoExecutionKey execution, List<IPluginExecutionMetadata>
     LinkedHashSet<String> sources = new LinkedHashSet<>();
     if(mappings != null && !mappings.isEmpty()) {
       for(IPluginExecutionMetadata mapping : mappings) {
-        if(mapping instanceof LifecycleMappingMetadataSource metadata) {
+        LifecycleMappingMetadataSource metadata = ((PluginExecutionMetadata) mapping).getSource();
+        if(metadata != null) {
           Object source = metadata.getSource();
           if(source instanceof String s) {
             sources.add(s);