Disable incremental builds for sccache

.gitea/actions/rust-cache/action.yml

@@ -96,6 +96,7 @@ runs:
         set -euo pipefail
         echo "enabled=true" >> "$GITHUB_OUTPUT"
         echo "RUSTC_WRAPPER=sccache" >> "$GITHUB_ENV"
+        echo "CARGO_INCREMENTAL=0" >> "$GITHUB_ENV"
         echo "SCCACHE_IGNORE_SERVER_IO_ERROR=1" >> "$GITHUB_ENV"
         echo "SCCACHE_IDLE_TIMEOUT=3600" >> "$GITHUB_ENV"
         echo "SCCACHE_LOG=${SCCACHE_LOG:-warn}" >> "$GITHUB_ENV"

README.md

@@ -66,6 +66,8 @@ Omit `sccache-bucket` to use the runner-local sccache cache:
 
 - Do not pass secret values as action inputs. Pass standard AWS environment
   variables from workflow secrets.
+- `CARGO_INCREMENTAL=0` is set because Rust incremental artifacts are not a
+  good fit for sccache-backed CI builds.
 - `SCCACHE_IGNORE_SERVER_IO_ERROR=1` is set so a cache outage falls back to
   local compilation instead of failing the build.
 - `SCCACHE_IDLE_TIMEOUT=3600` keeps the server alive across long build/test