Slack integration for Sentry issues mashes newlines in the issue message together without even a space

### Environment SaaS (https://sentry.io/) ### Steps to Reproduce 1. Set up Sentry integration for Slack to post new issues 2. Generate an issue that contains multiple lines of text in the message, separated by newlines ### Expected Result On both the Sentry web UI and the Slack message, the lines of text should be separated. Probably it's best if they are kept as separate lines, but if not then some separator like " / " or at the very least a space should be used. ### Actual Result The message looks fine in the web UI, but the lines are smushed together in Slack, making the message harder to read. Web UI:  Slack integration:  ### Product Area Settings - Integrations ### Link https://deck.sentry.io/issues/4340848096/?project=1490451&referrer=slack ### DSN https://bcb39434a3cf4daabb1934148b6799da@o265227.ingest.sentry.io/1490451 ### Version _No response_