Interchanged theme of buttons in Get Involved page

[safesurfer]

The color of the buttons are interchanged for Visit the DevHub and Sign Up buttons in Get Involved page.

Expected:
Visit the DevHub button should be Default
Sign Up button should be Dark

Actual:
Visit the DevHub button is Dark
Sign Up button is Default

Note: Sign Up button in the footer also needs to be changed to Dark

[calumcraig]

Tested on Netlify preview: https://deploy-preview-394--keen-stonebraker-bb1a10.netlify.com/get-involved/

Can see the buttons referenced above are now the expected colours:

[calumcraig]

QA verified.

Moving to done.