Warn for duplicate `browserTracingIntegrations`

[mydea]

Based on #16028, we should warn if multiple types of browserTracingIntegration are added. this can happen if you e.g. follow the react docs, where we tell you to replace the default one with the more specific react router one. If users leave the generic one in, weird things may happen.

[github-actions]

A PR closing this issue has just been released 🚀

This issue was referenced by PR #16042, which was included in the 9.13.0 release.