Update yml to use current_severity_label

What does this MR do and why?

Describe in detail what your merge request does and why.

Address this error: https://sentry.gitlab.net/gitlab/triage-ops/issues/4047534/?query=is%3Aunresolved

/builds/gitlab-org/quality/triage-ops/vendor/ruby/2.7.0/gems/gitlab-triage-1.25.0/lib/gitlab/triage/resource/context.rb:31:in `eval': undefined local variable or method `severity_label_name' for #<Gitlab::Triage::Resource::Issue:0x00005599b359f6d0> (NameError)
Did you mean?  severity_label_added_date
	from /builds/gitlab-org/quality/triage-ops/vendor/ruby/2.7.0/gems/gitlab-triage-1.25.0/lib/gitlab/triage/resource/context.rb:25:in `instance_eval'

which was broken by my previous commit(sorry): 8b8f54bd

In this commit I removed the severity_label_name method and replaced with current_severity_label

closes: #1166 (closed)

Expected impact & dry-runs

Please check this dry-run job for output, the job should exceed successfully and you should find the following note(among a few other ones):

# https://gitlab.com/gitlab-org/charts/gitlab/-/issues/3545

@twk3 @dorrino
This ~"FedRAMP Milestone::Vuln Remediation" ~"severity::3" issue will breach its 90 day remediation SLO in the current milestone.
Consider taking action before this becomes a ~"Remediation SLO::Breach" in 20 days (2022-12-13).
/label ~"Remediation SLO::Current Milestone"

it should not error out complaining about severity_label_name.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-with-a-dry-run on how to perform dry-runs.

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review