[Glitch] Ensure tabIndex is number instead of string

Port ec0c104bf2 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/features/ui/components/onboarding_modal.jsx

@@ -299,7 +299,7 @@ class OnboardingModal extends React.PureComponent {
                 <div
                   key={`dot-${i}`}
                   role='button'
-                  tabIndex='0'
+                  tabIndex={0}
                   data-index={i}
                   onClick={this.handleDot}
                   className={className}