fix(tracing): Make sure idle transaction does not override other transactions

[AbhiPrasad]

See: #7660

Make sure that if another transaction is set on the scope while an idle transaction is occuring, don't forcefully remove that transaction from the scope on idle transaction finish.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.73 KB (+0.01% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	64.75 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.28 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	57.23 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.84 KB (0%)
@sentry/browser - Webpack (minified)	68.2 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.87 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	48.69 KB (-0.01% 🔽)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	28.31 KB (-0.03% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.53 KB (-0.02% 🔽)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	44.88 KB (+0.01% 🔺)
@sentry/replay - Webpack (gzipped + minified)	38.86 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	63.58 KB (-0.02% 🔽)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	56.62 KB (0%)