chore: Correct title for v8 changelog (#17329)

Merged #17327 before
I could include these changes

Author: AbhiPrasad

docs/changelog/v8.md

@@ -1,6 +1,6 @@
-# Changelog for Sentry SDK 7.x
+# Changelog for Sentry SDK 8.x
 
-Sentry SDK v8 is no longer supported. We recommend migrating to the latest version of the SDK. You can migrate
+Support for Sentry SDK v8 will be dropped soon. We recommend migrating to the latest version of the SDK. You can migrate
 from `v8` of the SDK to `v9` by following the [migration guide](../migration/v8-to-v9.md).
 
 ## 8.55.0