Add release changelog fragment for cardano-api 11.4.0.0

Author: github-actions[bot]

.changes/20260806_181756_cardano-api_github-actions[bot]_cardano_api_11_4_0_0.yml

@@ -0,0 +1,5 @@
+description: Release cardano-api 11.4.0.0
+kind:
+- release
+pr: 1281
+project: cardano-api