Cypress.env deprecation / cy.env addition

## Current behavior

- The example directory [examples/env](https://github.com/cypress-io/github-action/tree/master/examples/env) uses the [Cypress.env()](https://docs.cypress.io/api/cypress-api/env) API call to get environment variables in tests. These are non-secret environment variables. The related workflow [example-env.yml](https://github.com/cypress-io/github-action/blob/master/.github/workflows/example-env.yml) refers to this usage in comments.

- PR https://github.com/cypress-io/cypress/pull/33181 indicates that Cypress plans to deprecate [Cypress.env()](https://docs.cypress.io/api/cypress-api/env) and introduce `cy.env()` in a future release.

## Desired behavior

- Follow developments in Cypress and migrate usage of [Cypress.env()](https://docs.cypress.io/api/cypress-api/env) as appropriate, and at an appropriate time, to avoid demonstrating any deprecated API usage and instead demonstrate handling environment variables according to updated recommendations.