[tests-only] Run PHP tests with 7.4-ubuntu20.04

[phil-davis]

Description

WIP - replaces #40172

Related Issue

#38348

How Has This Been Tested?

CI

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Database schema changes (next release will require increase of minor version instead of patch)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Technical debt
• [x] Tests only (no source changes)

Checklist:

• [ ] Code changes
• [ ] Unit tests added
• [ ] Acceptance tests added
• [ ] Documentation ticket raised:
• [ ] Changelog item, see TEMPLATE

[sonarqubecloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[phil-davis]

See #40292