[CircularProgress] Fix centering

[fiws]

caused by non default font-size. I tested this with the local documentation (increased font-size for testing)

i basically just applied the diff in this comment

• I have followed (at least) the PR section of the contributing guide.

Closes #17464

[mui-pr-bot]

Details of bundle changes.

Comparing: 788bd98...4b25142

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	0.00%	-0.00%	331,960	331,962	90,636	90,633
@material-ui/core/Paper	0.00%	0.00%	68,660	68,660	20,458	20,458
@material-ui/core/Paper.esm	0.00%	0.00%	62,098	62,098	19,203	19,203
@material-ui/core/Popper	0.00%	0.00%	28,397	28,397	10,159	10,159
@material-ui/core/Textarea	0.00%	0.00%	5,082	5,082	2,132	2,132
@material-ui/core/TrapFocus	0.00%	0.00%	3,766	3,766	1,596	1,596
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	16,348	16,348	5,818	5,818
@material-ui/core/useMediaQuery	0.00%	0.00%	2,488	2,488	1,050	1,050
@material-ui/lab	0.00%	0.00%	154,783	154,783	46,921	46,921
@material-ui/styles	0.00%	0.00%	51,420	51,420	15,288	15,288
@material-ui/system	0.00%	0.00%	15,581	15,581	4,351	4,351
Button	0.00%	0.00%	78,633	78,633	24,021	24,021
Modal	0.00%	0.00%	14,542	14,542	5,114	5,114
Portal	0.00%	0.00%	2,907	2,907	1,318	1,318
Rating	0.00%	0.00%	69,963	69,963	21,856	21,856
Slider	0.00%	0.00%	75,084	75,084	23,184	23,184
colorManipulator	0.00%	0.00%	3,835	3,835	1,519	1,519
docs.landing	0.00%	0.00%	52,232	52,232	13,768	13,768
docs.main	0.00%	0.00%	597,951	597,951	190,941	190,941
packages/material-ui/build/umd/material-ui.production.min.js	0.00%	-0.00%	302,847	302,849	87,081	87,078

Generated by 🚫 dangerJS against 4b25142

[oliviertassinari]

@fiws Thanks