fix(spanner): end spans for read-write methods (#3629)

Author: harshachinta

google-cloud-spanner/src/main/java/com/google/cloud/spanner/DatabaseClientImpl.java

@@ -294,6 +294,8 @@ public TransactionManager transactionManager(TransactionOption... options) {
       span.setStatus(e);
       span.end();
       throw e;
+    } finally {
+      span.end();
     }
   }
 

google-cloud-spanner/src/test/java/com/google/cloud/spanner/DatabaseClientImplTest.java

@@ -4006,7 +4006,10 @@ public void testTransactionManager_usesOptions() {
     when(pool.getSession()).thenReturn(session);
     TransactionOption option = mock(TransactionOption.class);
 
-    DatabaseClientImpl client = new DatabaseClientImpl(pool, mock(TraceWrapper.class));
+    TraceWrapper traceWrapper =
+        new TraceWrapper(Tracing.getTracer(), OpenTelemetry.noop().getTracer(""), false);
+
+    DatabaseClientImpl client = new DatabaseClientImpl(pool, traceWrapper);
     try (TransactionManager ignore = client.transactionManager(option)) {
       verify(session).transactionManager(option);
     }