Bump downstream dependencies in CI (#15685)

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

.github/workflows/ci.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c207d78..4e4b96a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -415,8 +415,8 @@
             PATH: mitmproxy
           - DOWNSTREAM: scapy
             REPO: secdev/scapy
-            # Latest commit on the scapy master branch, as of Sep 21, 2026.
-            REF: 51665737ea927b058edfc2535ec21abe94d3f8cb
+            # Latest commit on the scapy master branch, as of Sep 22, 2026.
+            REF: 8eb959aee35b7cb8e4060506df69d3a58c8fbf21
             PATH: scapy
           - DOWNSTREAM: sigstore-python
             REPO: sigstore/sigstore-python