Automatic toolchain upgrade to nightly-2025-10-20 (#4421)

Update Rust toolchain from nightly-2025-10-19 to nightly-2025-10-20
without any other source changes.

Co-authored-by: tautschnig <[email protected]>

Author: github-actions[bot]

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2025-10-19"
+channel = "nightly-2025-10-20"
 components = ["llvm-tools", "rustc-dev", "rust-src", "rustfmt"]