[doc] Update changelog for 2.1.4 [skip ci] (dmlc#11241)

Author: trivialfis

doc/changes/v2.1.0.rst

@@ -1,3 +1,13 @@
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+2.1.4 Patch Release (2025 Feb 6)
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+
+The 2.1.4 patch release incorporates the following fixes on top of the 2.1.3 release:
+
+- XGBoost is now compatible with scikit-learn 1.6 (#11021, #11162)
+- Build wheels with CUDA 12.8 and enable Blackwell support (#11187, #11202)
+- Adapt to RMM 25.02 logger changes (#11153)
+
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 2.1.3 Patch Release (2024 Nov 26)
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