Clarify Slack messaging for low code coverage

[rmtolmach]

Summary

This PR intends to make the warning message for low code coverage more clear. During a meeting Rachal and I had with Curt, he expressed that "target" was ambiguous.

Related issue(s)

None. Called out during a meeting. Too small of a change to warrant a ticket.

Testing done

None. I will keep an eye on the notifications channel, #platform-cop-be-ci-pipeline-failures, to make sure the messaging looks right.

Screenshots

This is the message being updated in this PR:

What areas of the site does it impact?

None. Alerting only.

Acceptance criteria

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• Events are being sent to the appropriate logging solution
• Documentation has been updated (link to documentation)
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Feature/bug has a monitor built into Datadog (if applicable)
• If app impacted requires authentication, did you login to a local build and verify all authenticated routes work as expected
• I added a screenshot of the developed feature

[Copilot]

Pull request overview

This PR updates the GitHub Actions CI Slack notification content to make the “low coverage” warning clearer by replacing the ambiguous “target” wording with an explicit threshold and adding more context about when deployments become blocked.

Changes:

• Updates the warning Slack header text from “Below Target” to “Below 93%”.
• Adds an explanatory note indicating that coverage below 90% will block CI/deployments.

[Copilot]

The warning header now highlights the 93% threshold, but the block still includes a field labeled ":dart: Required Minimum: 90%" (deployment block threshold). That combination can read as internally inconsistent (is the requirement 93% or 90%?). Consider renaming the 90% field to something explicit like “Deployment block threshold” / “Minimum to avoid deploy block”, and optionally adding a separate “Warning threshold: 93%” line for clarity.

[rmtolmach]

I think the fact that this is a "warning" makes it clear. But I'm open to other wording.

[Copilot]

This explanatory sentence is added as a "field" in a section that uses "fields" (2-column layout). In Slack Block Kit, fields will render in columns, so this note may appear squeezed into the left column next to “Current Coverage”, reducing readability. Consider making it its own section with a "text" value (full-width) above the fields list.

Suggested change

	"fields": [
	{
	"type": "mrkdwn",
	"text": "_If coverage dips below 90%, CI, including deployments, will be blocked._"
	},
	{
	"type": "mrkdwn",
	"text": {
	"type": "mrkdwn",
	"text": "_If coverage dips below 90%, CI, including deployments, will be blocked._"
	}
	},
	{
	"type": "section",
	"fields": [
	{
	"type": "mrkdwn",