Update tests using URL placeholder images to use the placeholderImage utility function

[driskull]

Priority impact

p - low

Test type

Update test

Which Component(s)

Carousel, custom-theme-stories.

Unstable Tests

Anything with placebear or palcem.at

Test error, if applicable

<style>
      .bg-image-example {
        color: red;
        background-image: url("https://placebear.com/3000/2000");
        background-size: cover;
        padding: 1rem;
        height: 300px;
        font-size: 32px;
        font-weight: 600;
        line-height: 32px;
      }
    </style>

PR skipped, if applicable

Additional Info

No response