test: try to make image test retryable

Uploading the existing file again would cause a conflict
resulting in retries failing.

Try to open the file instead and clear its content.

Signed-off-by: Max <max@nextcloud.com>

cypress/e2e/images.spec.js

@@ -198,8 +198,9 @@ describe('Test all image insertion methods', () => {
 	})
 
 	it('Upload images with the same name', () => {
-		cy.uploadFile('empty.md', 'text/markdown')
 		cy.openFile('empty.md')
+		// clear leftover content in case of a retry
+		cy.get('#viewer .ProseMirror').type('{ctrl}a{del}')
 
 		const assertImage = index => {
 			return clickOnImageAction(ACTION_UPLOAD_LOCAL_FILE)