Rsyslog can't write to sympa.conf log file because of missing permissions

Sympa is sending its log messages to rsyslogd, which is supposed to write them to /var/log/sympa.log. But this file is owned by sympa:sympa, so rsyslogd can't write to it. If it tries, you get errors like

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Dec 4 23:55:51 sympa-test rsyslogd: file '/var/log/sympa.log': open error: Permission denied [v8.2001.0 try https://www.rsyslog.com/e/2433 ]
Dec 4 23:55:51 sympa-test rsyslogd: action 'action-8-builtin:omfile' suspended (module 'builtin:omfile'), retry 0. There should be messages before this one giving the reason for suspension. [v8.2001.0 try https://www.rsyslog.com/e/2007 ]
Dec 4 23:55:51 sympa-test rsyslogd: action 'action-8-builtin:omfile' resumed (module 'builtin:omfile') [v8.2001.0 try https://www.rsyslog.com/e/2359 ]
Dec 4 23:55:51 sympa-test rsyslogd: action 'action-8-builtin:omfile' suspended (module 'builtin:omfile'), retry 0. There should be messages before this one giving the reason for suspension. [v8.2001.0 try https://www.rsyslog.com/e/2007 ]
Dec 4 23:55:51 sympa-test rsyslogd: action 'action-8-builtin:omfile' resumed (module 'builtin:omfile') [v8.2001.0 try https://www.rsyslog.com/e/2359 ]

(suspend-resumed repeated multiple times)
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in /var/log/syslog. Sympa's log messages go to syslog, too.

This could possibly solved in two ways. One is to hand sympa.log over to a fitting owner and group like syslog:adm. But I don't know whether or in what way Sympa itself needs access to sympa.log, so this might not be the best solution.

The second way is to extend the rsyslogd conf for Sympa in /etc/rsyslog.d/sympa.conf. You can set the file owner before the config and reset it after. This would look similar to

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$fileOwner sympa
:programname, contains, "sympa" /var/log/sympa.log
:programname, contains, "wwsympa" /var/log/sympa.log
:programname, contains, "archived" /var/log/sympa.log
:programname, contains, "bounced" /var/log/sympa.log
:programname, contains, "bulk" /var/log/sympa.log
:programname, contains, "task_manager" /var/log/sympa.log
$fileOwner root
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This problem appears in Ubuntu 20.04.1 with the package version sympa_6.2.40~dfsg-4.