fix: handled instana export safely when using experimental loader (#2227)

Prevented a runtime crash when using `--experimental-loader` with the v5 collector.

Author: aryamohanan

packages/collector/esm-loader.mjs

@@ -21,7 +21,10 @@
  */
 
 import instana from './src/index.js';
-instana();
+
+if (typeof instana === 'function') {
+  instana();
+}
 // Here we export all named exports from '@instana/core/iitm-loader.mjs', enabling
 // integration of import-in-the-middle (IITM) for Native ESM module support.
 export * from '@instana/core/iitm-loader.mjs';