cli: only pass through .mjs if ESM is supported

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/slow-bananas-beam.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Only allow pass through of `.mjs` in Jest transform if static ESM is supported.

packages/cli/config/jestSwcTransform.js

@@ -29,7 +29,7 @@ function createTransformer(config) {
     }
 
     // Skip transformation of .mjs files, they should only be used if ESM support is available
-    if (filePath.endsWith('.mjs')) {
+    if (jestOptions.supportsStaticESM && filePath.endsWith('.mjs')) {
       return { code: source };
     }