Bump github.com/swift-server/async-http-client

Bumps [github.com/swift-server/async-http-client](https://github.com/swift-server/async-http-client) from 1.13.1 to 1.15.0.
- [Release notes](https://github.com/swift-server/async-http-client/releases)
- [Commits](swift-server/async-http-client@1.13.1...1.15.0)

---
updated-dependencies:
- dependency-name: github.com/swift-server/async-http-client
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

Demo/SublimationDemoServer/Package.resolved

@@ -5,8 +5,8 @@
       "kind" : "remoteSourceControl",
       "location" : "https://github.com/swift-server/async-http-client.git",
       "state" : {
-        "revision" : "5bee16a79922e3efcb5cea06ecd27e6f8048b56b",
-        "version" : "1.13.1"
+        "revision" : "864c8d9e0ead5de7ba70b61c8982f89126710863",
+        "version" : "1.15.0"
       }
     },
     {