docs: correct and extend ping debug instructions

[MikeMcC399]

Issue

The README > Debugging waiting for URL to respond contains an example:

$ node src/ping-cli.js https://example.cypress.io
pinging url https://example.cypress.io for 30 seconds
::debug::pinging https://example.cypress.io has finished ok

where the last line of the example is incorrect.

Without debugging enabled, the output under Node.js v20.18.0 LTS appears as:

$ node src/ping-cli.js https://example.cypress.io
pinging url https://example.cypress.io for 30 seconds

With debugging enabled, the output is as follows:

$ DEBUG='@cypress/github-action' node src/ping-cli.js https://example.cypress.io
pinging url https://example.cypress.io for 30 seconds
  @cypress/github-action total ping timeout 60000 +0ms
  @cypress/github-action individual ping timeout 30000ms +0ms
  @cypress/github-action retries limit 2 +0ms
  @cypress/github-action pinging https://example.cypress.io has finished ok after 185ms +185ms

Change

Provide correct instructions in README > Debugging waiting for URL to respond for running node src/ping-cli.js in debug and non-debug mode.

[cypress-app-bot]

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[github-actions]

🎉 This PR is included in version 6.7.7 🎉

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