test: clean up warnings about unclosed connections in test (#4199)

Change-Id: Ie68df6368d6daaff7f8c81d6f6f2f7dd04d5ea13

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [ ] Make sure to open an issue as a [bug/issue](https://togithub.com/googleapis/java-bigtable-hbase/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)

Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://togithub.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

Author: igorbernstein2

bigtable-hbase-1.x-parent/bigtable-hbase-1.x/src/test/java/com/google/cloud/bigtable/hbase1_x/TestBigtableConnection.java

@@ -40,6 +40,7 @@
 import org.apache.hadoop.hbase.TableName;
 import org.apache.hadoop.hbase.client.Connection;
 import org.apache.hadoop.hbase.util.Bytes;
+import org.junit.After;
 import org.junit.AfterClass;
 import org.junit.Before;
 import org.junit.BeforeClass;
@@ -86,13 +87,20 @@ public void setUp() throws IOException {
     connection = new BigtableConnection(configuration);
   }
 
+  @After
+  public void tearDown() throws Exception {
+    if (connection != null) {
+      connection.close();
+    }
+  }
+
   @Test
   public void testOverloadedConstructor() throws IOException {
-    Connection hbaseConnection =
-        new BigtableConnection(configuration, false, Executors.newSingleThreadExecutor(), null);
-
-    assertTrue(hbaseConnection.getAdmin() instanceof BigtableAdmin);
-    assertTrue(hbaseConnection.getTable(TABLE_NAME) instanceof AbstractBigtableTable);
+    try (Connection hbaseConnection =
+        new BigtableConnection(configuration, false, Executors.newSingleThreadExecutor(), null)) {
+      assertTrue(hbaseConnection.getAdmin() instanceof BigtableAdmin);
+      assertTrue(hbaseConnection.getTable(TABLE_NAME) instanceof AbstractBigtableTable);
+    }
   }
 
   @Test