Bump downstream dependencies in CI (pyca#14241)

Co-authored-by: pyca-boringbot[bot] <pyca-boringbot[bot]+106132319@users.noreply.github.com>

Author: pyca-boringbot[bot]

.github/workflows/ci.yml

@@ -453,8 +453,8 @@ jobs:
             PATH: josepy
           - DOWNSTREAM: mitmproxy
             REPO: mitmproxy/mitmproxy
-            # Latest commit on the mitmproxy main branch, as of Jan 12, 2026.
-            REF: a7621021191011de7c95771459688de3ecd67c10
+            # Latest commit on the mitmproxy main branch, as of Jan 31, 2026.
+            REF: a9c3dafa0f10a8cb36e8453ce91575f92a53e841
             PATH: mitmproxy
           - DOWNSTREAM: scapy
             REPO: secdev/scapy