Drop global rustc-wrapper = sccache from .cargo/config.toml

The sdist job in publish-python.yml doesn't compile any Rust and
therefore doesn't install sccache, but cargo metadata still reads the
workspace config and invokes the wrapper — causing a fatal "No such
file or directory" before it can even enumerate packages.

Same fix rationale as the target-cpu=native removal: config.toml is
read everywhere cargo runs, so it can't assume specific host tooling.
Build jobs that want sccache opt in explicitly via
mozilla-actions/sccache-action or maturin-action's sccache: true.

Author: darmie

.cargo/config.toml

@@ -7,7 +7,11 @@ incremental = false
 # Configure the number of parallel jobs
 jobs = 8
 
-rustc-wrapper = "sccache"
+# Deliberately no global `rustc-wrapper = "sccache"`: that breaks any
+# environment that hasn't installed sccache (e.g. the sdist step of
+# our Python publish workflow). If you want sccache locally, either
+# set `CARGO_BUILD_RUSTC_WRAPPER=sccache` in your shell, or add a
+# `~/.cargo/config.toml` override outside this repository.
 
 
 [target.'cfg(all())']