text: Title: Elapsed time is not updated when merging results
  Body: `rebot` of RF7 produces an incorrect total suite runtime when merging results - compared to RF6.
  
  With some lines of bash, I created a reproducable example where I execute the following steps with both RF6 and 7:
  1. Run the suite with `-v FAIL:yes` so that the first test case will FAIL. Test 2 and 3 have a sleep time of 0.111s.
  2. Re-run the failed one with `--rerunfailed`, this time the first test case PASSES with a sleep time of 1s.
  3. Merge the first and the second XML.
  
  The final HTML log `rebot_1_2.html` can be seen in the version number inside the results folder.
  RF6 (left) looks good to me: the "merged" total suite runtime is the sum of
  - first run: 0.112 (T2) + 0.113 (T3) = 0.225s
  - second run with the re-executed 1st Test: 1.001 (T1)
  - = in total: 1.226
  
  RF7 (right) however shows a total runtime of 0.242s, which seems to be just the total suite runtime of the first run.
  
  ![image](https://github.com/robotframework/robotframework/assets/1897410/6e9e3e3f-f28b-4b9e-9c2e-de1afbfc1f03)
  
  You can find the script, the Pipfile and the XML/HTML logs in the attached zip file.
  [rebot-test.zip](https://github.com/robotframework/robotframework/files/14343227/rebot-test.zip)
  