CI: github actions: switch to stable LibreSSL release

LibreSSL-3.3.0 appeared to have its own bugs, it is development release,
let us switch to stable LibreSSL-3.2.4 instead
diff --git a/.github/matrix.py b/.github/matrix.py
index a5ce191..3489833 100644
--- a/.github/matrix.py
+++ b/.github/matrix.py
@@ -105,7 +105,7 @@
         "stock",
         "OPENSSL_VERSION=1.0.2u",
         "LIBRESSL_VERSION=2.9.2",
-        "LIBRESSL_VERSION=3.3.0",
+        "LIBRESSL_VERSION=3.2.4",
         "BORINGSSL=yes",
     ]:
         flags = ["USE_OPENSSL=1"]