Updating release notes for 4.5.3.0

Author: foundationdb-ci

docs/sphinx/source/ReleaseNotes.md

@@ -7,6 +7,22 @@ As the [versioning guide](Versioning.md) details, it cannot always be determined
 
 ## 4.5
 
+### 4.5.3.0
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+
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+**[Full Changelog (4.5.2.0...4.5.3.0)](https://github.com/FoundationDB/fdb-record-layer/compare/4.5.2.0...4.5.3.0)**
+
+#### Mixed Mode Test Results
+
+Mixed mode testing run against the following previous versions:
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+❌`4.4.7.0`, ❌`4.4.8.0`, ❌`4.4.9.0`, ❌`4.4.10.0`, ❌`4.4.11.0`, ✅`4.4.12.0`, ✅`4.4.14.0`, ✅`4.4.15.0`, ✅`4.5.1.0`, ✅`4.5.2.0`
+
+[See full test run](https://github.com/FoundationDB/fdb-record-layer/actions/runs/16629945151)
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+
+
 ### 4.5.2.0
 
 <h4> Bug Fixes </h4>