Updates for tfc-agent release 1.15.4 (#104)

Author: claire-tfc

website/docs/cloud-docs/agents/changelog.mdx

@@ -18,6 +18,12 @@ within each release are categorized into one or more of the following labels:
 Each version below corresponds to a release artifact available for download on
 the official [releases website](https://releases.hashicorp.com/tfc-agent/).
 
+## 1.15.4 (07/24/2024)
+
+SECURITY:
+
+* Moved to building with Go 1.22.5 in which several CVEs are addressed (#727)
+
 ## 1.15.3 (07/10/2024)
 
 SECURITY: