Update activesupport from 6.0.3.4 to 7.0.4

What does this MR do?

Updates activesupport gem from 6.0.3.4 to 7.0.4, which is used only from rubocop-rails gem, which is required only by gitlab-styles gem.

Related issues

Slightly related to #3430 (closed)

Refs.

Our projects (like GDK and -docs, as far as I know) are already with activesupport 7.0.x due to upgrading gitlab-styles to 9.0. Also gitlab-org/release-tools is now with activesupport 7.0 but without gitlab-styles.

• Update gitlab-styles to v9 (gitlab-org/gitlab-development-kit!2747 - merged)
• Update dependency gitlab-styles to v9 (gitlab-org/gitlab-docs!3094 - merged)
• Update dependency activesupport to v7 (gitlab-org/release-tools!1831 - merged)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• [n/a] Documentation created/updated
• [n/a] Tests added
• [n/a] Integration tests added to GitLab QA
• [n/a] Equivalent MR/issue for omnibus-gitlab opened