ci: update nightly toolchain version to 2025-10-01

Signed-off-by: Jérémy Audiger <[email protected]>

Author: jaudiger

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
 
 env:
-  NIGHTLY_TOOLCHAIN: nightly-2025-11-01
+  NIGHTLY_TOOLCHAIN: nightly-2025-10-01
 
 jobs:
   check: