Update comment about Weaver slot assertion

Explain more clearly why this assertion is important.

Test: comment-only change
Bug: 356324437
Change-Id: I0ef2862fb6fbb062520c98935d347f1445a7dfae
Merged-In: I0ef2862fb6fbb062520c98935d347f1445a7dfae
(cherry picked from commit b267fcced5994e89afdfcb7387e9f9fa56c6852d)
1 file changed