Fix db test leak warning.

core-util/src/test/java/org/signal/core/util/SQLiteDatabaseExtensionsTest.kt

@@ -10,6 +10,7 @@ import androidx.sqlite.db.SupportSQLiteOpenHelper
 import assertk.assertThat
 import assertk.assertions.isEqualTo
 import assertk.assertions.isNotNull
+import org.junit.After
 import org.junit.Assert.assertArrayEquals
 import org.junit.Before
 import org.junit.Test
@@ -50,6 +51,11 @@ class SQLiteDatabaseExtensionsTest {
       .run()
   }
 
+  @After
+  fun cleanUp() {
+    db.close()
+  }
+
   @Test
   fun `update - content values work`() {
     val updateCount: Int = db.writableDatabase