Update Free Named Arguments Section After Change in Process Library

[luprochazka-cen63872]

Section : 2.5.2.7 Free Named Arguments
RF 7.3 Release notes: Enhancements to the Process library

At least the example is not suitable. The stdout=ping_output.txt and stderr=ping_error.txt are not free named argument ** configuration anymore.

[pekkaklarck]

Yeah, Process.Run Process nowadays accepts named-only arguments, not free named arguments. See robotframework/robotframework#5412 for details.

At least String.Format String still uses free named args and due to the nature of the keyword it won't be changed.