fix: harmonize npm name usage in logs

[MikeMcC399]

This PR modifies the action source file index.js for consistency with

• the npm documentation About npm which uses lower case npm and with
• the Cypress documentation Module API which does not include NPM in its name

Changes

• Text and comments now refer to npm consistently in lower case.
• NPM is removed from the reference to the Cypress Module API

[MikeMcC399]

• This PR is left in draft state pending merge of PR docs: add pnpm and Yarn to intro #887

It is the last PR in a series concerned with adding pnpm and Yarn to the list of supported package manager lockfiles supported for installation. This small change triggered a whole lot of other changes making sure that npm was consistently referred to.

When this PR is merged it will trigger an npm release and that will also update the README on https://www.npmjs.com/package/@cypress/github-action, so before that happens all the other documentation changes should have completed.

For some strange reason the README on https://github.com/marketplace/actions/cypress-io is updated even without a release, except that the display of the value of the released version number is only updated with a release to the GitHub Marketplace!

[MikeMcC399]

Please review. Thanks.

[MikeMcC399]

Rebased and ready again 🙂

[github-actions]

🎉 This PR is included in version 5.7.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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