[ci] Roll pinned nightly toolchain

[google-pr-creation-bot]

Automated changes by create-pull-request GitHub action

[gemini-code-assist]

Summary of Changes

Hello @google-pr-creation-bot, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request performs an automated update to the project's CI configuration, specifically rolling forward the pinned-nightly Rust toolchain. This ensures that the project's automated tests and builds are run against a current nightly compiler, maintaining compatibility and leveraging the latest developments in the Rust ecosystem.

Highlights

• CI Toolchain Update: The pinned nightly Rust toolchain version used in continuous integration (CI) has been updated to a more recent date.

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[gemini-code-assist]

Code Review

This pull request automatically updates the pinned nightly Rust toolchain. However, the proposed version nightly-2025-10-26 appears to be an invalid toolchain identifier, which will cause continuous integration builds to fail. I have left a critical comment on the Cargo.toml file detailing this issue. This should be corrected to a valid toolchain version before merging.

[gemini-code-assist]

The specified nightly toolchain nightly-2025-10-26 is not a valid, available toolchain. This will cause CI builds that rely on the nightly toolchain to fail. Please update this to a valid, existing nightly toolchain version. This issue may stem from a bug in the automation script that created this pull request.