0. emacs -Q
1. C-x C-f test.html RET
2. C-c C-t html RET Test RET
=> error in skeleton-internal-1: Symbol’s value as variable is void: resume:

I believe this bug was introduced by this commit:

commit e038a7571ddb9ec2110533fdd1b359150939c58c
Author:     Stefan Monnier <monnier@iro.umontreal.ca>
Commit:     Stefan Monnier <monnier@iro.umontreal.ca>
CommitDate: Thu Aug 6 18:45:33 2020 -0400

    * lisp/skeleton.el: Use lexical-binding

The following patch fixes the bug, at least for the above recipe.