fix: resolve CodeQL alerts #24 and #26 (#4145)

**[#24](https://github.com/MagicMirrorOrg/MagicMirror/security/code-scanning/24)
– `js/class.js`**

`fnTest` works by serialising a function to a string and checking if
`"xyz"` appears in it - the function is never actually called. The bare
`xyz;` is never executed, so CodeQL is right to flag it. `return xyz;`
makes the intent clear. So this is purely a cosmetic change.


**[#26](https://github.com/MagicMirrorOrg/MagicMirror/security/code-scanning/26)
– `tests/e2e/helpers/global-setup.js`**

CodeQL flagged `if (exec) exec;` as a useless expression - and it was
right. But the real find was one level deeper.

`startApplication` hardcoded `const port = 8080`, so `MM_PORT` was
always overwritten before the app started. The test named "Set port 8100
on environment variable MM_PORT" was actually testing port 8080 the
whole time - it just happened to pass anyway.

Removed the dead `exec` parameter, made `startApplication` read
`MM_PORT` from the environment, and fixed the test so it actually checks
what it says it checks.

js/class.js

@@ -11,7 +11,7 @@
 (function () {
 	let initializing = false;
 	const fnTest = (/xyz/).test(function () {
-		xyz;
+		return xyz;
 	})
 		? /\b_super\b/
 		: /.*/;