🐛 Fix .codecov.yaml

[rsimha]

We recently enabled PR statuses from codecov in order to improve AMP's code coverage. It appears the settings in .codecov.yaml are not taking effect.

PR comments:

• Comments are supposed to be disabled. Yet they're being posted. For example: Move shared CSS from ampdoc.css to ampelement.css #22494 (comment)

amphtml/.codecov.yml

Lines 3 to 4 in 9c4ec35

	# See https://docs.codecov.io/docs/pull-request-comments
	comment: off

PR statuses:

• The failure threshold is supposed to be 100% (so all PRs pass). Yet, PRs are failing when coverage reduces by even a fraction of a percent. For example: Move shared CSS from ampdoc.css to ampelement.css #22494 (comment)

amphtml/.codecov.yml

Lines 6 to 16 in 9c4ec35

	# See https://docs.codecov.io/v4.3.0/docs/commit-status
	coverage:
	status:
	project:
	base: auto # Use base commit for PRs, parent commit for push builds
	target: auto # Target same coverage as the base / parent commit
	threshold: 100 # Passing check no matter what the coverage is
	patch:
	base: auto # Use base commit for PRs, parent commit for push builds
	target: 100 # Target 100% coverage for diffs
	threshold: 100 # Passing check no matter what the coverage is

This PR rewrites the .codecov.yaml file using the latest recommended format at https://docs.codecov.io/docs

[rsimha]

This worked.

Merging to unblock incoming PRs.