deps(rust-proxy): update mockall requirement from 0.14.0 to 0.15.0 in /rust/letterbox-proxy in the rust-proxy group

[dependabot]

Updates the requirements on mockall to permit the latest version.
Updates mockall to 0.15.0

Changelog

Sourced from mockall's changelog.

[ 0.15.0 ] - 2026-06-28

Added

• Compatibility with the #[auto_impl] macro. (#686)

[ 0.14.0 ] - 2025-11-22

Added

• Allow mocking structs and traits with const generics. (#649)

• Compatibility with the #[trait_variant::make] macro. (#640)

• Allow Expectations with a non-exact call count to be used in Sequences. (#660)

Changed

• The MSRV is now Rust 1.77.0. (#650)

Fixed

• No longer poison a static mock method's internal Mutex when panicing, even when using a stable Rust compiler. Also, no longer poison it even if there is no Context object. For example, if the user never set an Expectation at all. (#650)

• Suppress single-use-lifetimes lints in the generated code, for cases where the orginal code wouldn't have triggered the warning. (#627)

• Fix mocking foreign functions with a variadic argument and no pattern, for example fn foo(...) as opposed to fn bar(x: ...). That worked in prior versions of Mockall only until Rust 1.93.0, which made such arguments illegal for Rust functions. (#673)

• Fully qualify Send and Sync traits in generated code, allowing structs named Send or Sync to be in scope without conflicts. (#672)

[ 0.13.1 ] - 2024-11-17

Fixed

... (truncated)

Commits

• fc2c853 chore: Release
• 551fadd Merge pull request #688 from asomers/audit-job-lockfile
• 21529e3 Fix the audit CI job
• 2270cdb Merge pull request #686 from Kranzes/automock-auto_impl-compat
• d3b041d Add compatibility with the #[auto_impl] macro
• 055886e Merge pull request #687 from asomers/clippy-june-2026
• ed4bf07 Clippy cleanup
• f7a4d6f Merge pull request #685 from asomers/clippy=may-2026
• ba15180 Clippy cleanup: useless_borrows_in_formatting
• de22d57 Merge pull request #684 from asomers/github-workflows
• Additional commits viewable in compare view

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