interface: Tweak the tooltip of the "Show process properties" button
requested to merge automerisnaranja/gnome-system-monitor:process-properties-button-tooltip into master
"Tooltip labels should be short and written in header capitalization".
https://developer.gnome.org/hig/patterns/feedback/tooltips.html?highlight=tooltip
Change the tooltip to "Process Properties" to follow the guidelines.
It's something that I missed from !84 (merged)