bug#41353: (const x) is a thunk

[Jan Synacek]

With guile-3.0.2:

scheme@(guile-user)> (thunk? (const 1))
$1 = #t

Since thunk is a procedure that does not accept arguments (section
6.9.7, documentation for 'thunk?'), the result of the above evaluation
should be #f.