`ERROR: Closing data source tag` in filename of datetime output

[casesolved-co-uk]

Checklist before starting to submit this bug report

I confirm that:

• [X] I am submitting a bug report! :)
• [X] I have tested this with the latest stable Snoopy version (or the latest master build).
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• [X] I have read Snoopy's documentation here and here.
• [X] I have searched Snoopy issues for an existing issue that matches my problem, and found none.

Bug description

Got the following file in /var/log when I enabled logging to file with the datetime format:

snoopy.log-[ERROR: Closing data source tag ('}') not found.]

Bug reproduction steps

1. Ubuntu 20.04.06 LTS (AWS version)
2. Install using install-snoopy.sh as root (version 2.5.1)
3. reconfigure to output using: output = file:/var/log/snoopy.log-%{datetime:%Y-%m-%d}
4. disable and enable snoopy
5. View file in /var/log

Expected result

Normal filename

Actual result

Strange filename above