@actions/artifact: convert to an ESM module

packages/artifact/src/internal/shared/user-agent.ts

@@ -1,9 +1,9 @@
-// eslint-disable-next-line @typescript-eslint/no-var-requires, @typescript-eslint/no-require-imports
-const packageJson = require('../../../package.json')
+// Version is hardcoded to avoid issues with import.meta.url in Jest
+const VERSION = '6.0.0'
 
 /**
  * Ensure that this User Agent String is used in all HTTP calls so that we can monitor telemetry between different versions of this package
  */
 export function getUserAgentString(): string {
-  return `@actions/artifact-${packageJson.version}`
+  return `@actions/artifact-${VERSION}`
 }