Bug 1944474 [wpt PR 50360] - Use assert_throws_js in content-security…

…-policy/securitypolicyviolation/source-file.html, a=testonly

Automatic update from web-platform-tests
Use assert_throws_js in content-security-policy/securitypolicyviolation/source-file.html (#50360)

Currently it's using the pattern

`try { ...; assert_unreached(); } catch (e) {}`

but then the assertion thrown by assert_unreached() is ignored by the catch.
--

wpt-commits: 9b9efcb6e431c7c82555f64a03029b397ec3fb72
wpt-pr: 50360

testing/web-platform/tests/content-security-policy/securitypolicyviolation/source-file.html

@@ -22,11 +22,7 @@
       eval('');
       //# sourceURL=${input}
     `)
-    try {
-      eval(trusted_script);
-      assert_unreached();
-    } catch (e) {}
-
+    assert_throws_js(EvalError, _ => eval(trusted_script));
     assert_equals((await violation).sourceFile, output);
   }, description);
 };