Add CI coverage

[mmicko]

Generate XML coverage report and attach it to build.
Fail CI if coverage is bellow 90%

[github-actions]

File	Coverage
All files	90%	✅
src/yosys_mau/__init__.py	100%	✅
src/yosys_mau/stable_set.py	98%	✅
src/yosys_mau/config_parser/__init__.py	100%	✅
src/yosys_mau/config_parser/_commands.py	94%	✅
src/yosys_mau/config_parser/_low_level.py	94%	✅
src/yosys_mau/config_parser/_options.py	91%	✅
src/yosys_mau/config_parser/_sections.py	89%	❌
src/yosys_mau/config_parser/_values.py	91%	✅
src/yosys_mau/source_str/__init__.py	93%	✅
src/yosys_mau/source_str/re.py	93%	✅
src/yosys_mau/source_str/report.py	96%	✅
src/yosys_mau/task_loop/__init__.py	100%	✅
src/yosys_mau/task_loop/_task.py	90%	✅
src/yosys_mau/task_loop/context.py	78%	❌
src/yosys_mau/task_loop/job_server.py	91%	✅
src/yosys_mau/task_loop/job_server_helper.py	100%	✅
src/yosys_mau/task_loop/logging.py	81%	❌
src/yosys_mau/task_loop/priority.py	86%	❌
src/yosys_mau/task_loop/process.py	89%	❌

Minimum allowed coverage is 90%

Generated by 🐒 cobertura-action against 634ee8e