Describe the bug

According to Nix Manual and the stdenv.mkDerivation source, meta.position is specified by stdenv.mkDerivation according to several attributes of the package.

As meta.position is also used to update packages automatically, it is sometimes necessary to specify/override with a canonical value. A real-world example can be found in #295828. However, such overriding via <pkg>.overrideAttrs provided by stdenv.mkDerivation seems simply discarded.

Steps To Reproduce

$ nix repl
Welcome to Nix 2.18.1. Type :? for help.

nix-repl> pkgs = import ./. { }

nix-repl> pkgs.hello.meta.position
"/home/shamrock/Projects/NixOS/nixpkgs_timeshift/pkgs/by-name/he/hello/package.nix:34"

nix-repl> pkgs.cowsay.meta.position
"/home/shamrock/Projects/NixOS/nixpkgs_timeshift/pkgs/tools/misc/cowsay/default.nix:46"

nix-repl> (pkgs.hello.overrideAttrs (previousAttrs: { meta = previousAttrs.meta // { position = pkgs.cowsay.meta.position; }; })).meta.position
"/home/shamrock/Projects/NixOS/nixpkgs_timeshift/pkgs/by-name/he/hello/package.nix:34"

Or
nix eval --impure --expr "let pkgs = import ./. { }; in (pkgs.hello.overrideAttrs (previousAttrs: { meta = previousAttrs.meta // { position = pkgs.cowsay.meta.position; }; })).meta.position"

Expected behavior

The meta.position attribute be overridable with <pkg>.overrideAttrs, i.e.

$ nix eval --impure --expr "let pkgs = import ./. { }; in (pkgs.hello.overrideAttrs (previousAttrs: { meta = previousAttrs.meta // { position = pkgs.cowsay.meta.position; }; })).meta.position == pkgs.cowsay.meta.position"
true

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