CI: Github Actions: enable USE_QUIC=1 for BoringSSL builds

if haproxy is built against BoringSSL, let us add USE_QUIC=1 dynamically
diff --git a/.github/matrix.py b/.github/matrix.py
index 577ad5b..067ce93 100644
--- a/.github/matrix.py
+++ b/.github/matrix.py
@@ -109,6 +109,8 @@
         "BORINGSSL=yes",
     ]:
         flags = ["USE_OPENSSL=1"]
+        if ssl == "BORINGSSL=yes":
+            flags.append("USE_QUIC=1")
         if ssl != "stock":
             flags.append("SSL_LIB=${HOME}/opt/lib")
             flags.append("SSL_INC=${HOME}/opt/include")