chore: slightly improve code samples

Author: ava12

spanner/src/cancel_backup.php

@@ -55,6 +55,8 @@ function cancel_backup_operation($instanceId, $databaseId)
     printf('Cancel backup operation complete.' . PHP_EOL);
 
     // Operation may succeed before cancel() has been called. So we need to clean up created backup.
-    $backup->delete();
+    if ($backup->exists()) {
+        $backup->delete();
+    }
 }
 // [END spanner_cancel_backup_create]

spanner/src/list_backups.php

@@ -79,7 +79,7 @@ function list_backups($instanceId)
     }
 
     // List backups that were created after a timestamp that are also ready.
-    $createTime = $spanner->timestamp(new \DateTime('-1 hour'));
+    $createTime = $spanner->timestamp(new \DateTime('-1 day'));
     print("All backups created after $createTime:" . PHP_EOL);
     $filter = "create_time >= \"$createTime\" AND state:READY";
     foreach ($instance->backups(['filter' => $filter]) as $backup) {

spanner/src/list_database_operations.php

@@ -27,7 +27,7 @@
 use Google\Cloud\Spanner\SpannerClient;
 
 /**
- * List all database operations in an instance.
+ * List all optimize restored database operations in an instance.
  * Example:
  * ```
  * list_database_operations($instanceId);

spanner/test/spannerTest.php

@@ -651,19 +651,18 @@ public function testListBackupOperations()
     }
 
     /**
-     * @depends testListBackupOperations
+     * @depends testCreateBackup
      */
     public function testListBackups()
     {
         $output = $this->traitRunCommand('list-backups', [
             'instance_id' => self::$instanceId,
         ]);
         $this->assertContains(self::$backupId, $output);
-        $this->assertContains(self::$backupId . '-pro', $output);
     }
 
     /**
-     * @depends testListBackups
+     * @depends testCreateBackup
      */
     public function testUpdateBackup()
     {