phpExtensions.soap: back to doCheck = false (except on Darwin)

On *-linux we get:
> FAILED TEST SUMMARY
> ---------------------------------------------------------------------
> SOAP Bug #71610 - Type Confusion Vulnerability - SOAP / make_http_soap_request() [tests/bug71610.phpt]
> Bug #76348 (WSDL_CACHE_MEMORY causes Segmentation fault) [tests/bugs/bug76348.phpt]
Logs e.g.: https://github.com/NixOS/nixpkgs/pull/330299/checks?check_run_id=27989364591

pkgs/top-level/php-packages.nix

@@ -644,6 +644,7 @@ in {
           configureFlags = [
             "--enable-soap"
           ];
+          doCheck = stdenv.isDarwin;  # TODO: a couple tests still fail on *-linux
           internalDeps = [ php.extensions.session ];
           patches = lib.optionals (lib.versions.majorMinor php.version == "8.2" && lib.versionOlder php.version "8.2.22") [
             # Fixes compatibility with libxml2 2.13. Part of 8.3.10RC1+, 8.2.22RC1+