Updating release notes for 4.8.5.0

Author: foundationdb-ci

docs/sphinx/source/ReleaseNotes.md

@@ -7,6 +7,22 @@ As the [versioning guide](Versioning.md) details, it cannot always be determined
 
 ## 4.8
 
+### 4.8.5.0
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+
+
+**[Full Changelog (4.8.4.0...4.8.5.0)](https://github.com/FoundationDB/fdb-record-layer/compare/4.8.4.0...4.8.5.0)**
+
+#### Mixed Mode Test Results
+
+Mixed mode testing run against the following previous versions:
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+❌`4.6.2.0`, ❌`4.6.3.0`, ❌`4.6.4.0`, ❌`4.6.5.0`, ❌`4.7.1.0`, ❌`4.7.2.0`, ✅`4.7.3.0`, ✅`4.8.1.0`, ✅`4.8.2.0`, ✅`4.8.3.0`
+
+[See full test run](https://github.com/FoundationDB/fdb-record-layer/actions/runs/18949783608)
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+
+
 ### 4.8.4.0
 
 <h4> New Features </h4>