[SG-35155] Code monitoring ARC checklist issues

Created by: gitstart-sourcegraph

closes https://github.com/sourcegraph/sourcegraph/issues/35156

Description

• Change Code Monitoring header to use H2 (instead of H1)
• Add role=img for Icon in page header breadcrumb.

Refs

SoureGraph Issue GitStart Link

Test plan

• Confirm checks in description are available on Code Monitor page
• Confirm there are no UI changes

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.