test: update e2e update test to include content in css file

When there is no contents the test fail with `Expected [ Entry({ level: SEVERE, message: 'http://localhost:39559/styles.css - Failed to load resource: net::ERR_CONTENT_LENGTH_MISMATCH', timestamp: 1710924490251, type: '' }) ] not to contain <jasmine.objectContaining(Object({ level: SEVERE }))>.`

Author: alan-agius4

tests/legacy-cli/e2e/assets/15.0-project/src/styles.css

@@ -1 +1,5 @@
 /* You can add global styles to this file, and also import other style files */
+
+body {
+  margin: 0;
+}