Add release changelog fragment for cardano-rpc 11.3.0.0

Author: github-actions[bot]

.changes/20260904_075351_cardano-rpc_github-actions[bot]_cardano_rpc_11_3_0_0.yml

@@ -0,0 +1,5 @@
+description: Release cardano-rpc 11.3.0.0
+kind:
+- release
+pr: 1330
+project: cardano-rpc