[wdio-allure-reporter] Unable to attach buffer content type as a 'image/png' to allure report

[jaworsmi]

webdriverio/packages/wdio-allure-reporter/src/index.js

Lines 538 to 540 in 6351905

	static addAttachment = (name, content, type = 'application/json') => {
	if (typeof content === 'string' || Buffer.isBuffer(content)) {
	type = 'text/plain'

All kind of buffer content types (like screenshots created in wdio) are handed as a 'text/plain' due to changes made in #6022

[mgrybyk]

Fixing it.
Adding unit tests already