Fix broken link to incident management roles

Why is this change being made?

Update to fix broken link to new location here: /handbook/engineering/infrastructure/incident-management/#roles-and-responsibilities

URL path for incident management roles has been changed, now the link 404s

https://about.gitlab.com/handbook/engineering/infrastructure/team/reliability/incident-management/

Does this MR meet the acceptance criteria?

If the pipeline is successful, yes! 🤞

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what