pre-commit: Add libiconv for tests on x86_64-darwin

Note: not a checkInput, because we need
this dependency in the role of a _build_
input during tests: library path, etc.

Solves

    E                 = note: ld: library not found for -liconv
    E                         clang-11: error: linker command failed with exit code 1 (use -v to see invocation)
    E
    E
    E               error: failed to compile `rust-hello-world v0.1.0 (/private/tmp/nix-build-python3.9-pre-commit-2.18.1.drv-1/pytest-of-nixbld4/pytest-0/popen-gw3/test_rust_hook0/0/.pre-commit/repomj5itq00)`, intermediate artifacts can be found at `/private/tmp/nix-build-python3.9-pre-commit-2.18.1.drv-1/pytest-of-nixbld4/pytest-0/popen-gw3/test_rust_hook0/0/.pre-commit/repomj5itq00/target`
    E
    E               Caused by:
    E                 could not compile `rust-hello-world` due to previous error

    pre_commit/util.py:146: CalledProcessError

in test case

    FAILED tests/repository_test.py::test_rust_hook

1 files changed, 6 insertions, 0 deletions

diff --git a/pkgs/tools/misc/pre-commit/default.nix b/pkgs/tools/misc/pre-commit/default.nix
index 72f7f66c9e43a..addd7134b7f88 100644
--- a/pkgs/tools/misc/pre-commit/default.nix
+++ b/pkgs/tools/misc/pre-commit/default.nix
@@ -6,6 +6,7 @@
 , dotnet-sdk
 , git
 , go
+, libiconv
 , nodejs
 }:
 
@@ -54,6 +55,11 @@ buildPythonPackage rec {
     re-assert
   ];
 
+  buildInputs = [
+    # Required for rust test on x86_64-darwin
+    libiconv
+  ];
+
   doCheck = true;
 
   postPatch = ''