python312Packages.mobi: exclude standard-imghdr to fix build

Our `standard-*` packages are set up to be null on the Python versions
that still include the corresponding module in the standard library.
However, since mobi depends on standard-imghdr unconditionally, using
the package on versions of Python that still have imghdr in the standard
library fails to build due to the following sequence of steps:

1. Something calls `python312Packages.mobi`.
2. `standard-imghdr` in the dependencies resolves to `null`, since
   `imghdr` is still in the standard library on Python 3.12 and we have
   the `standard-imghdr` package set to be null on versions of Python
   where `imghdr` is in the standard library.
3. `pythonRuntimeDepsCheck` runs.
4. `pythonRuntimeDepsCheck` sees `Requires-Dist: standard-imghdr` in
   mobi's distinfo metadata and checks whether the package is installed.
5. It is not, so the runtime deps check fails the build.

We solve this issue by removing `standard-imghdr` from the list of
dependencies on versions of Python where the package is set to `null`
(those versions that have `imghdr` in the standard library). The package
continues to work because it will transparently import the standard
library version of `imghdr`.

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

@@ -6,6 +6,7 @@
   hatchling,
   standard-imghdr,
   pytestCheckHook,
+  pythonOlder,
 }:
 
 buildPythonPackage rec {
@@ -29,6 +30,8 @@ buildPythonPackage rec {
     standard-imghdr
   ];
 
+  pythonRemoveDeps = lib.optionals (pythonOlder "3.13") [ "standard-imghdr" ];
+
   nativeCheckInputs = [
     pytestCheckHook
   ];