dev/team: make ResolveByGitHubHandle case-insensitive
Created by: bobheadxi
Makes ResolveByGitHubHandle
case-insensitive when scanning for matching GitHub handles.
Example:
Noah has his handle provided in lowercase: https://github.com/sourcegraph/handbook/blob/main/data/team.yml#L422
GitHub handles aren't case sensitive, so this should be allowed
Test plan
n/a dev lib