CI: Add a dependency file for patman

Now that patman has an unusual dependency, add a requirements.txt file
and use it in CI

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/requirements.txt b/tools/patman/requirements.txt
index e8cbc6c..57a284d 100644
--- a/tools/patman/requirements.txt
+++ b/tools/patman/requirements.txt
@@ -1,3 +1,4 @@
+aiohttp==3.9.1
 ConfigParser==7.1.0
 importlib_resources==6.5.2
 pygit2==1.13.3