Fix DEPRECATION_HORIZON sed pattern in script/release

[joelhawksley]

Backport of the DEPRECATION_HORIZON sed fix from main (companion to #2691 on main).

Root cause

lib/view_component/deprecation.rb stores the value as a quoted string:

DEPRECATION_HORIZON = "4.0.0"

But script/release's sed was:

sed -E -i '' -e "s/DEPRECATION_HORIZON = [0-9]+/DEPRECATION_HORIZON = \$((major + 1))/g"

[0-9]+ requires ≥1 digit immediately after = , but the next character is the opening quote. So the substitution matched nothing and silently no-oped on every 3.x release — the horizon has never actually been bumped by the script.

Fix

Match the full quoted X.Y.Z and replace with "<major+1>.0.0", mirroring the fix I made on main.

Applicability of other main-branch release fixes

For reference, most of the recent main-branch release fixes do not apply to 3.x:

• 3.x has no release.yml, publish-release.yml, or push_gem.yml workflows — releases are done locally.
• script/release on 3.x is interactive-only (no CI-args branch) and doesn't call build_docs.
• script/publish on 3.x is just bundle exec rake release + gh-pages push — no gh release create, no check_github_permissions.

Only this sed bug is relevant. Verified locally on macOS with BSD sed: starting value "5.0.0" + major=3 → "4.0.0"; ruby -c reports Syntax OK.

[joelhawksley]

Superseded by the port PR (opening next), which includes this fix along with the full release-workflow port.