add PR link

Signed-off-by: inge4pres <[email protected]>

changelogs/8.15.asciidoc

@@ -17,6 +17,7 @@ https://github.com/elastic/apm-server/compare/v8.15.3\...v8.15.4[View commits]
 ==== Bug fixes
 
 - Rollover for all APM data streams is now executing correctly in Elasticsearch 8.15.4, fixing a https://www.elastic.co/guide/en/observability/current/apm-known-issues.html#_upgrading_to_v8_15_x_may_cause_ingestion_to_fail[known issue] present in 8.15.0, 8.15.1, 8.15.2 and 8.15.3.
+  The fix is applied through https://github.com/elastic/elasticsearch/pull/116219[elasticsearch#116219].
 
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 [[apm-release-notes-8.15.3]]