Strengthen the assertion in CallFunction, that only callable functions
(not class constructors) are passed.

Change-Id: I2dc2d061cdc9930b5b8926285f021f9772e97570
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3380529Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78585}