Create a note in session report only if QA issue is defined

MR attempts to fix the error we see in Slack:

An unexpected error occurred while reporting test results in issues.
The error occurred in job: https://ops.gitlab.net/gitlab-org/quality/staging/-/jobs/2890500
Gitlab::Error::BadRequest Server responded with code 400, message: 400 Bad request - Note {:note=>["can't be blank"]}. Request URI: https://gitlab.com/api/v4/projects/gitlab-org%2Fquality%2Ftestcase-sessions/issues/5220/notes

Assumption is that this error appears because test report is trying to add a relate quick action note "/relate #{Runtime::Env.qa_issue_url}" and GITLAB_QA_ISSUE_URL isn't defined. In the example above there is no QA issue as pipeline is being triggered on schedule and not by release bot.

• Related to https://gitlab.com/gitlab-org/gitlab-qa/-/merge_requests/622