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
```

0 files changed, 0 insertions, 0 deletions