Adding to what @Martino mentioned above here is the exact location to add that tag in log4net section:
<log4net debug="true">
<root>
<level value="ALL" />
<appender-ref ref="LogFileAppender" />
</root>
<appender name="LogFileAppender" type="log4net.Appender.FileAppender">
<file type="log4net.Util.PatternString" value="%property{LogFileName}" />
<appendToFile value="true" />
<lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date %level %logger - %message%newline" />
</layout>
</appender>
<logger additivity="false" name="Hangfire">
<level value="ERROR" />
<appender-ref ref="HangfireLoggerAppender" />
</logger>
</log4net>