curl: disable fetchpatch passthru test on darwin

`tests` seem to be something else on darwin, leading to an eval failure
on the instantiation of this test.

```
 … while evaluating the attribute 'tests.fetchpatch'

   at ./pkgs/tools/networking/curl/default.nix:182:7:

    181|       withCheck = finalAttrs.finalPackage.overrideAttrs (_: { doCheck = true; });
    182|       fetchpatch = tests.fetchpatch.simple.override { fetchpatch = (fetchpatch.override { fetchurl = useThisCurl fetchurl; }) // { version = 1; }; };
       |       ^
    183|       curlpp = useThisCurl curlpp;

 … while calling a functor (an attribute set with a '__functor' attribute)

   at ./pkgs/tools/networking/curl/default.nix:182:20:

    181|       withCheck = finalAttrs.finalPackage.overrideAttrs (_: { doCheck = true; });
    182|       fetchpatch = tests.fetchpatch.simple.override { fetchpatch = (fetchpatch.override { fetchurl = useThisCurl fetchurl; }) // { version = 1; }; };
       |                    ^
    183|       curlpp = useThisCurl curlpp;

 (stack trace truncated; use '--show-trace' to show the full trace)

 error: value is a function while a set was expected
```

1 files changed, 2 insertions, 1 deletions

diff --git a/pkgs/tools/networking/curl/default.nix b/pkgs/tools/networking/curl/default.nix
index 0351debfb3c1e..9cbf6dc1b0fb5 100644
--- a/pkgs/tools/networking/curl/default.nix
+++ b/pkgs/tools/networking/curl/default.nix
@@ -179,7 +179,6 @@ stdenv.mkDerivation (finalAttrs: {
     inherit opensslSupport openssl;
     tests = {
       withCheck = finalAttrs.finalPackage.overrideAttrs (_: { doCheck = true; });
-      fetchpatch = tests.fetchpatch.simple.override { fetchpatch = (fetchpatch.override { fetchurl = useThisCurl fetchurl; }) // { version = 1; }; };
       curlpp = useThisCurl curlpp;
       coeurl = useThisCurl coeurl;
       haskell-curl = useThisCurl haskellPackages.curl;
@@ -191,6 +190,8 @@ stdenv.mkDerivation (finalAttrs: {
       # nginx-http3 = useThisCurl nixosTests.nginx-http3;
       nginx-http3 = nixosTests.nginx-http3;
       pkg-config = testers.testMetaPkgConfig finalAttrs.finalPackage;
+    } // lib.optionalAttrs (!stdenv.isDarwin) {
+      fetchpatch = tests.fetchpatch.simple.override { fetchpatch = (fetchpatch.override { fetchurl = useThisCurl fetchurl; }) // { version = 1; }; };
     };
   };