v1.4.0

Minor release changes

• Add created_at column to swift_jobs.jobs table. #74

Patch release changes

• Default job cleanup to nil instead of default version of JobCleanup.

Other changes

• Uses hashes to reference actions instead of versions
• Upgrade GH action actions/checkout to v7.0.1.
• Use GH action vapor/swift-codecov-action for uploading coverage data.
• Update SECURITY.md