add tests for Footer component

[harisbikovic]

Related #390
This PR containes tests for the Footer component.

[szakhlypa]

I prefer to not depend on link's order.
What if we add some more accessibility into component with aria-label and use it in getByRole?
For example:
repository link in Footer.tsx:

  <a
    href={repoUrl}
    _other_props_here_
    aria-label={
      intl.formatMessage({
        id: "components.Footer.repositoryLinkLabel",
        defaultMessage: "GitHub",
      })
    }
  >
    <Icon icon="github" />
  </a>

And its test with getByRole

  const repositoryLink = screen.getByRole("link", { name: "GitHub" });
  expect(repositoryLink).toHaveAttribute("href", "https://github.com/edgehog-device-manager/edgehog");

Also, can we use different values for homepageUrl and repoUrl props in test to distinguish in case of error.

[szakhlypa]

Dot in RegExp matches any single character except line terminators, so we need to escape it with backslash. Otherwise test will pass even with appVersion="0x1x0-alphax1" property.

Suggested change

	const appVersionElement = screen.getByText(/0.1.0-alpha.1/);
	const appVersionElement = screen.getByText(/0\.1\.0-alpha\.1/);