Centre the loading spinners on the charts page

[github-actions[bot]]

Coverage report for air-quality-ui

St.:grey_question:	Category	Percentage	Covered / Total
🟢	Statements	94.42%	677/717
🟢	Branches	86.5%	173/200
🟢	Functions	88.04%	162/184
🟢	Lines	94.1%	622/661

Test suite run success

362 tests passing in 28 suites.

Report generated by 🧪jest coverage report action from e5dc5e4e71feb156579259808003af97d2f54d8c