Fix permission error in release pipeline

When making a (point) release, the [pipeline](https://gitlab.com/gromacs/gromacs/-/jobs/7697221097) launched by the `admin/make-release-build.py` script has been failing on the last step (archive:full-release), with the error message 
```
rsync: [generator] failed to set times on "/var/www/manual/.": Operation not permitted (1)
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1207) [sender=3.1.3]
```
indicating that the script doesn't have sufficient permissions when trying to preserve the time stamps during file transfer. This error hasn't been interfering with the release process much, but nevertheless it would be good to remove it to avoid confusion. 
As a simple fix, I removed the `-t` option from the `rsync` command as the time stamps aren't critical anyway.
Feel free to disregard this MR if your think it's unnecessary or feel that there's a better solution.

admin/make-release-build.py

@@ -127,7 +127,7 @@ def upload_files(
     Needs to have successfully set up SSH key infrastructure before.
     """
 
-    upload_command = ["rsync", "-rlptvP"]
+    upload_command = ["rsync", "-rlvP"]
     upload_command.extend(options)
 
     upload_command.append(str(path))