Protect: Update Scan History extension types

[dkmyta]

Fixes #
Historical scan results must use either "plugins"/"themes" for the extension types.

Proposed changes:

• Modify types received from endpoint accordingly.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

• https://github.com/Automattic/jetpack-scan-team/issues/1598

Does this pull request change what data or activity we track or use?

• No

Testing instructions:

• Run this branch of Protect on JT
• Review the scanHistory initial state property in your console and ensure that each applicable results now as "plugins" or "themes" for threats->extension->type

[github-actions]

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[nateweller]

Suggested change

	if ( ! empty( $source_threat->extension ) && in_array( $source_threat->extension->type, array( 'plugin', 'theme' ), true ) ) {
	$source_threat->extension->type .= 's';
	}
	// Protect's Extension_Model uses the plural form of "plugin" and "theme" extension types.
	if ( ! empty( $source_threat->extension ) && in_array( $source_threat->extension->type, array( 'plugin', 'theme' ), true ) ) {
	$source_threat->extension->type .= 's';
	}

[nateweller]

LGTM!