Jest coverage block

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<BlockComponent block={{"id":"covbot.file-coverage-block","title":"Jest coverage","matches":["*"],"description":"Display coverage, generated by Jest.","type":"file","entry":"./src/blocks/coverage-block.tsx","owner":"covbot","repo":"jest-coverage-block"}} context={{"repo":"jest-coverage-block","owner":"covbot","path":"example/report.json","sha":"main","file":"README.md"}} />