Go: Bump toolchain to 1.25.7

[mbg]

Updates the version of the Go toolchain we use for builds to 1.25.7.

The addition of com_github_stretchr_testify as a dependency in MODULE.bazel was automatic when I ran Bazel, probably a result of that dependency getting promoted to an explicit dependency in #21300

[Copilot]

Pull request overview

Updates the repository’s Go toolchain patch level to keep the Go extractor build/test environment aligned across go.mod, Bazel, and GitHub Actions.

Changes:

• Bump Go toolchain directive in go/extractor/go.mod from go1.25.0 to go1.25.7.
• Update the Go version default used by the Go extractor test composite action to ~1.25.7.
• Update Bazel rules_go SDK download to 1.25.7 and add the Bazel repo mapping for com_github_stretchr_testify from go.mod deps.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
go/extractor/go.mod	Advances the Go toolchain patch version for the extractor module.
go/actions/test/action.yml	Aligns CI test Go version default with the bumped toolchain patch level.
MODULE.bazel	Aligns Bazel’s Go SDK version with the bumped toolchain and ensures testify’s repo is available for Bazel builds/tests.