cargo-auditable-cargo-wrapper: don't wrap if cargo-auditable is meta.broken (#250615)

Recent changes to `cargo-auditable-cargo-wrapper` and `librsvg`
caused it to ignore the user's decision to opt out of `cargo-audit`
functionality, partially because `librsvg` does not use
`buildRustPackage`.

This commit restores the single-point-of-opt-out from this mis-named
functionality: `cargo-auditable.meta.broken`.

Co-authored-by: figsoda <[e-mail]>

pkgs/development/compilers/rust/cargo-auditable-cargo-wrapper.nix

···
 { lib, runCommand, makeBinaryWrapper, rust-audit-info, cargo, cargo-auditable }:
 
+if cargo-auditable.meta.broken then
+  cargo
+else
 runCommand "auditable-${cargo.name}" {
   nativeBuildInputs = [ makeBinaryWrapper ];