Update to source-highlight seems to have broken rust

[Kaelyn]

Hi Efraim and guix-devel,

Based on my local cuirass instance and some spot testing this morning, it 
appears the change to source-highlight in commit 367bc2d198 has broken the 
build of rust 1.73.
* `guix refresh -l source-highlight` reports modifying the package would 
require a large number of rebuilds ("Building the following 6129 packages would 
ensure 9069 dependent packages are rebuilt").
* I am seeing a consistent test failure for rust starting with that commit.
* `guix weather rust@1.73` reports 100% availability for both ci.guix.gnu.org 
and bordeaux.guix.gnu.org at commit fbeae77ae6 but 0% availability at commit 
367bc2d198.

The consistently-reported failure is:

---- metadata::cargo_metadata_non_utf8 stdout ----
thread 'metadata::cargo_metadata_non_utf8' panicked at 
crates/cargo-test-support/src/paths.rs:155:33:
failed to mkdir_p 
/tmp/guix-build-rust-1.73.0.drv-0/rustc-1.73.0-src/build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/tmp/cit/t1684/foo/�/./src:
 Invalid or incomplete multibyte or wide character (os error 84)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    metadata::cargo_metadata_non_utf8

test result: FAILED. 2801 passed; 1 failed; 198 ignored; 0 measured; 0 filtered 
out; finished in 92.81s

error: test failed, to rerun pass `--test testsuite`


I don't exactly understand how wrapping scripts in source-highlight ended up 
breaking the above rust test, nor do I use rust, so I wanted to bring it to 
folks' attention since the failure appears to affect a great many packages (I 
noticed it in an ffmpeg build failure on my local cuirass instance).

Cheers,
Kaelyn