Update aiosignal requirement from >=1.3.0 to >=1.4.0 in /src/a2a

Updates the requirements on [aiosignal](https://github.com/aio-libs/aiosignal) to permit the latest version.
- [Release notes](https://github.com/aio-libs/aiosignal/releases)
- [Changelog](https://github.com/aio-libs/aiosignal/blob/master/CHANGES.rst)
- [Commits](aio-libs/aiosignal@v1.3.0...v1.4.0)

---
updated-dependencies:
- dependency-name: aiosignal
  dependency-version: 1.4.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

src/a2a/requirements_a2a.txt

@@ -1,4 +1,4 @@
-fastapi>=0.104.0
+fastapi>=0.104.0
 uvicorn[standard]>=0.24.0
 starlette>=0.27.0
 pydantic>=2.5.0
@@ -7,4 +7,4 @@ httpx>=0.25.0
 psutil>=5.9.0
 prometheus-client>=0.19.0
 gunicorn>=21.2.0
-aiosignal>=1.3.0
+aiosignal>=1.4.0