[pyproject.toml] Use relative_files option for coverage to avoid long names in...

[pyproject.toml] Use relative_files option for coverage to avoid long names in CI-generated coverage reports
4 jobs for coverage-uses-relative-files in 28 minutes and 14 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #243693
docker
build_linux_37

00:27:37

68.0%
passed #243694
docker
build_linux_38

00:26:47

69.0%
passed #243691
intel macos
build_macos_intel_37

00:28:08

68.0%
passed #243692
intel macos
build_macos_intel_38

00:26:31

69.0%