Fix Windows CI failure due to GPG signature verification

Emacs 29 on Windows fails to verify GPG signatures from the nongnu
ELPA archive when installing buttercup. Disable package-check-signature
in CI environments to work around this.

Also remove the s.el test dependency from Eldev since we replaced
s-index-of with cl-position in de898ed.

Author: bbatsov

Eldev

@@ -8,7 +8,12 @@
 
 (eldev-use-plugin 'autoloads)
 
-(eldev-add-extra-dependencies 'test 'paredit 's 'buttercup)
+(eldev-add-extra-dependencies 'test 'paredit 'buttercup)
+
+;; Disable GPG signature verification for package installation in CI.
+;; Emacs 29 on Windows fails to verify signatures from the nongnu ELPA archive.
+(when (getenv "CI")
+  (setq package-check-signature nil))
 
 (setq byte-compile-docstring-max-column 240)
 (setq checkdoc-force-docstrings-flag nil)