Added missing token in CI

[cmaglie]

Please check if the PR fulfills these requirements

See how to contribute

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)
• configuration.schema.json updated if new parameters are added.

What kind of change does this PR introduce?

Added a missing token to avoid CI failures:

Run bufbuild/buf-action@v1
  with:
    pr_comment: false
    lint: false
    format: false
    breaking: false
    breaking_against: .git#branch=origin/master,subdir=rpc
    domain: buf.build
    github_actor: cmaglie
    github_token: ***
    setup_only: false
    exclude_imports: false
    breaking_against_registry: false
    push: true
    push_disable_create: false
    archive: false
  env:
    GO_VERSION: 1.24
Using the latest release of buf: 1.55.1
Downloading buf (1.55.1)
Setup buf (1.55.1) at /opt/hostedtoolcache/buf/1.55.1/x64
/opt/hostedtoolcache/buf/1.55.1/x64/buf config ls-modules --format name
buf.build/arduino/arduino-cli
/opt/hostedtoolcache/buf/1.55.1/x64/buf build --error-format github-actions
/opt/hostedtoolcache/buf/1.55.1/x64/buf push --error-format github-actions --exclude-unnamed --git-metadata --source-control-url https://github.com/arduino/arduino-cli/commit/ae68728ffb883cde81566383e7ce97b0adfe0301 --create
Failure: you are not authenticated for buf.build. Set the BUF_TOKEN environment variable or run "buf registry login", using a Buf API token as the password. For details, visit https://buf.build/docs/bsr/authentication
Error: Failed push

What is the current behavior?

What is the new behavior?

Does this PR introduce a breaking change, and is titled accordingly?

Other information