python3Packages.httpx: unset SSL_CERT_FILE in hook

This fixes downstream test failures.

pkgs/development/python-modules/httpx/default.nix

@@ -108,6 +108,10 @@ buildPythonPackage rec {
 
   __darwinAllowLocalNetworking = true;
 
+  # stdenv's fake SSL_CERT_FILE breaks default http transport constructor with:
+  # FileNotFoundError: [Errno 2] No such file or directory
+  setupHook = ./setup-hook.sh;
+
   meta = with lib; {
     changelog = "https://github.com/encode/httpx/blob/${src.rev}/CHANGELOG.md";
     description = "Next generation HTTP client";

pkgs/development/python-modules/httpx/setup-hook.sh

@@ -0,0 +1,5 @@
+httpxSslCertFileUnset() {
+    unset SSL_CERT_FILE
+}
+
+postHooks+=(httpxSslCertFileUnset)