[ci] Roll pinned nightly toolchain

[google-pr-creation-bot]

On failure, consider manually creating roll PRs for previous nightlies to bisect the failure.

[gemini-code-assist]

Summary of Changes

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This pull request rolls the pinned nightly Rust toolchain to a newer version. This update necessitated adjustments to several UI test .stderr files, as the compiler's error messages for unsatisfied trait bounds have become more precise, now including explicit trait suggestions and helpful implementation notes.

Highlights

• Nightly Toolchain Roll: The pinned-nightly Rust toolchain has been updated from nightly-2026-01-25 to nightly-2026-02-25 in Cargo.toml.
• UI Test Error Message Updates: Several UI test .stderr files were updated to reflect changes in how the Rust compiler reports unsatisfied trait bound errors, now providing more specific trait suggestions and help notes.

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Changelog

• Cargo.toml
  • Updated the pinned-nightly toolchain version to nightly-2026-02-25.
• zerocopy-derive/tests/ui/derive_transparent.nightly.stderr
  • Adjusted expected error messages to reflect more precise trait bound suggestions and help notes.
• zerocopy-derive/tests/ui/enum.nightly.stderr
  • Adjusted expected error messages to reflect more precise trait bound suggestions and help notes.
• zerocopy-derive/tests/ui/late_compile_pass.nightly.stderr
  • Adjusted expected error messages to reflect more precise trait bound suggestions and help notes.
• zerocopy-derive/tests/ui/mid_compile_pass.nightly.stderr
  • Adjusted expected error messages to reflect more precise trait bound suggestions and help notes.
• zerocopy-derive/tests/ui/msrv_specific.nightly.stderr
  • Adjusted expected error messages to reflect more precise trait bound suggestions and help notes.
• zerocopy-derive/tests/ui/struct.nightly.stderr
  • Adjusted expected error messages to reflect more precise trait bound suggestions and help notes.

Activity

• Automated roll of the pinned nightly toolchain by google-pr-creation-bot.
• The PR description provides guidance for manual intervention if the automated roll fails, suggesting bisecting failures by creating PRs for previous nightlies.

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[gemini-code-assist]

Code Review

This pull request updates the pinned nightly Rust toolchain and the corresponding UI test stderr files. While updating the test outputs is expected with a toolchain roll, there is a critical issue in Cargo.toml. The pinned-nightly version uses the year 2026, which is in the future. This will cause CI to fail when attempting to download a non-existent toolchain.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.87%. Comparing base (b7fc71d) to head (9ca09ea).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3070   +/-   ##
=======================================
  Coverage   91.87%   91.87%           
=======================================
  Files          20       20           
  Lines        6057     6057           
=======================================
  Hits         5565     5565           
  Misses        492      492           

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