update another test comment (2)

Co-authored-by: Mythicaeda <[email protected]>

db-tests/src/test/java/gov/nasa/jpl/aerie/database/ExternalEventTests.java

@@ -1603,8 +1603,7 @@ void externalEventSourceBounds() throws SQLException {
     }
 
     /**
-     * Within a derivation group two sources can bear the same key, but they can across different derivation groups (and
-     *    therefore different source types).
+     * Source names must be unique within a derivation group; they can repeat across derivation groups.
      */
     @Test
     void duplicateSource() throws SQLException {