ssl: update cert rotation deadline (#14119)

## DESCRIBE YOUR PR
Move up the date for this maintenance to the Thursday before. This
balances giving customers advanced notice with making sure we have time
to proceed with fallbacks if we encounter an issue.

## IS YOUR CHANGE URGENT?  

Help us prioritize incoming PRs by letting us know when the change needs
to go live.
- [ ] Urgent deadline (GA date, etc.): <!-- ENTER DATE HERE -->
- [x] Other deadline: 2025-07-03
- [ ] None: Not urgent, can wait up to 1 week+

## PRE-MERGE CHECKLIST

*Make sure you've checked the following before merging your changes:*

- [x] Checked Vercel preview for correctness, including links
- [x] PR was reviewed and approved by any necessary SMEs (subject matter
experts)
- [x] PR was reviewed and approved by a member of the [Sentry docs
team](https://github.com/orgs/getsentry/teams/docs)

Author: keeakita

docs/security-legal-pii/security/ssl.mdx

@@ -46,7 +46,7 @@ This suite of protocols and ciphers represents Sentry's official support; howeve
 
 <Alert title="Note" level="warning">
 
-Starting on 2025-07-21, the following domains with certificates previously issued by DigiCert will be transitioned to being issued by Let's Encrypt:
+Starting on 2025-07-17, the following domains with certificates previously issued by DigiCert will be transitioned to being issued by Let's Encrypt:
 
 - `sentry.io`
 - `de.sentry.io`