build: Run size-limit action on master

[AbhiPrasad]

We need to run size-limit on master so that we upload size assets that we can do comparisons with.

Some formatting fixes climbed in, but ${{ github.event_name == 'pull_request' }} || ${{ startsWith(github.ref, 'refs/heads/master/') }} is the line to care about.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.3 KB (added)
@sentry/browser - ES5 CDN Bundle (minified)	59.72 KB (added)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	17.91 KB (added)
@sentry/browser - ES6 CDN Bundle (minified)	52.67 KB (added)
@sentry/browser - Webpack (gzipped + minified)	19.67 KB (added)
@sentry/browser - Webpack (minified)	64.04 KB (added)
@sentry/react - Webpack (gzipped + minified)	19.69 KB (added)
@sentry/nextjs Client - Webpack (gzipped + minified)	43.85 KB (added)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	25.64 KB (added)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	23.91 KB (added)

[Lms24]

I think the formatting changes were already added in #5318 but should be fine either way.