cubicweb #3203391 [session] demote log level in session.close (from info to debug) [validation pending]

Can yield too much log traffic.

prioritynormal
typebug
done in3.17.10
load0.100
load left0.000
closed by#b39ac464e3ac [server/session] demote log to debug
patch[server/session] demote log to debug [applied]