github: move CARGO_* CI variables into Cargo configuration

`incremental` is unnecessary since the `rust-toolchain` action
already sets the environment variable, but probably harmless for
future‐proofing.

Author: emilazy

.cargo/config-ci.toml

@@ -1,3 +1,7 @@
+[profile.dev]
+debug = "none"
+incremental = false
+
 # NOTE: on Windows, build with the static CRT, so that produced .exe files don't
 # depend on vcruntime140.dll; otherwise the user requires visual studio if they
 # download a raw .exe

.github/workflows/ci.yml

@@ -14,10 +14,6 @@ concurrency:
 
 permissions: {}
 
-env:
-  CARGO_INCREMENTAL: 0
-  CARGO_PROFILE_DEV_DEBUG: 0
-
 jobs:
   test:
     strategy: