Closes #98: LCP test for checking fetchpriority fails consistently

[jeawhanlee]

Description

Fixes the issue where LCP test for checking fetchpriority fails consistenly.

Fixes #98

Documentation

Technical documentation

it is important to break down whole steps into small steps for easy testing and better code readability

Type of change

• [x] Bug fix (non-breaking change which fixes an issue).

New dependencies

None

[jeawhanlee]

I have ran test at least 2x to see that it passes.

[MathieuLamiot]

Tested on my side:

• When no error it passes.
• when manually introducing an error on the page (missing image), it fails.