Upgrade CI workflows to Go 1.26

[Copilot]

This updates the repository’s GitHub Actions workflows to the latest stable Go release line. CI now exercises the two most recent major Go versions, while lint and release jobs move to Go 1.26.

• CI matrix

  • Advances the test matrix from Go 1.23/1.24 to 1.25/1.26
  • Keeps coverage across current and previous stable majors rather than pinning to older releases

• Release workflow

  • Moves the release job from Go 1.24 to 1.26
  • Aligns release builds with the current stable toolchain

• Lint workflow

  • Updates actions/setup-go from 1.24.x to 1.26.x
  • Keeps static analysis on the same toolchain family as release

• Example

  strategy:
    matrix:
      go: [ '1.25', '1.26' ]