refactor(core): apply lint rule cred-class-field-unobscured-sensitive-input (#4495)

* ⬆️ Upgrade linter

* 📦 Update `package-lock.json`

* 👕 Enable rule

* 👕 Apply rule

* 📦 Re-update `package-lock.json`

packages/nodes-base/credentials/MailgunApi.credentials.ts

@@ -37,6 +37,7 @@ export class MailgunApi implements ICredentialType {
 			displayName: 'API Key',
 			name: 'apiKey',
 			type: 'string',
+			typeOptions: { password: true },
 			default: '',
 		},
 	];