chore(tidb): archive log if test not successful (#3028)

### **User description**
archive log if test not successful, eg test timeout


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### **PR Type**
enhancement


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### **Description**
- Modified the post-build action in the `ghpr_mysql_test.groovy`
pipeline script to archive logs if the test is unsuccessful instead of
only on failure.



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### **Changes walkthrough** 📝
<table><thead><tr><th></th><th align="left">Relevant
files</th></tr></thead><tbody><tr><td><strong>Enhancement</strong></td><td><table>
<tr>
  <td>
    <details>
<summary><strong>ghpr_mysql_test.groovy</strong><dd><code>Archive logs
if test is unsuccessful instead of failure</code>&nbsp; &nbsp;
</dd></summary>
<hr>

pipelines/pingcap/tidb/latest/ghpr_mysql_test.groovy

<li>Changed the post-build action from <code>failure</code> to
<code>unsuccessful</code> for <br>archiving artifacts.<br>


</details>


  </td>
<td><a
href="https://github.com/PingCAP-QE/ci/pull/3028/files#diff-1a06f14532e2be1eefc21763f67d1a83b63ab9740c315b30ae4132768be19121">+1/-1</a>&nbsp;
&nbsp; &nbsp; </td>

</tr>                    
</table></td></tr></tr></tbody></table>

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Signed-off-by: purelind <purelind@gmail.com>

pipelines/pingcap/tidb/latest/ghpr_mysql_test.groovy

@@ -118,7 +118,7 @@ pipeline {
                             always {
                                 junit(testResults: "**/result.xml")
                             }
-                            failure {
+                            unsuccessful {
                                 archiveArtifacts(artifacts: 'tidb-test/mysql_test/mysql-test.out*', allowEmptyArchive: true)
                             }
                         }