while: Restore tolerance of condition error

Since !6442 (merged) we correctly reject the code

set(paren "(")
while(${paren})
endwhile()

However, rejecting it breaks compatibility with projects that used such code accidentally. In CMake 3.21 and below, any error in the condition was ignored because the false result exited the loop first. Restore tolerance of the error for now. A policy will be needed to make it an error later.

Note that the same condition with if was always correctly rejected.

Fixes: #22524 (closed)
Issue: #23296 (closed)
Backport: release
Topic-rename: while-bug-compatibility