ci: Fix auto-release regex

[mydea]

Based on e.g. https://github.com/getsentry/sentry-javascript/actions/runs/4135873735/jobs/7148935627 you can see that head_ref is actually just the branch name without refs/heads

[Lms24]

Good catch!

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.06 KB (0%)
@sentry/browser - ES5 CDN Bundle (minified)	62.19 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.69 KB (+0.01% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	55.33 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.42 KB (0%)
@sentry/browser - Webpack (minified)	66.77 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.45 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	47.85 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.97 KB (0%)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.23 KB (0%)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	42.28 KB (0%)
@sentry/replay - Webpack (gzipped + minified)	36.7 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	59.93 KB (-0.02% 🔽)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	53.48 KB (0%)