[SPARK-29851][SQL][FOLLOW-UP] Use foreach instead of misusing map

### What changes were proposed in this pull request?

This PR proposes to use foreach instead of misusing map as a small followup of #26476. This could cause some weird errors potentially and it's not a good practice anyway. See also SPARK-16694

### Why are the changes needed?
To avoid potential issues like SPARK-16694

### Does this PR introduce any user-facing change?
No

### How was this patch tested?
Existing tests should cover.

Closes #26729 from HyukjinKwon/SPARK-29851.

Authored-by: HyukjinKwon <[email protected]>
Signed-off-by: HyukjinKwon <[email protected]>

Author: HyukjinKwon

sql/catalyst/src/test/scala/org/apache/spark/sql/connector/InMemoryTableCatalog.scala

@@ -180,8 +180,8 @@ class InMemoryTableCatalog extends BasicInMemoryTableCatalog with SupportsNamesp
   }
 
   override def dropNamespace(namespace: Array[String]): Boolean = {
-    listNamespaces(namespace).map(dropNamespace)
-    listTables(namespace).map(dropTable)
+    listNamespaces(namespace).foreach(dropNamespace)
+    listTables(namespace).foreach(dropTable)
     Option(namespaces.remove(namespace.toList)).isDefined
   }
 }