[ci] Bump number of shards for test_build to 10

[poteto]

I noticed test_build can take a while so let's bump the number of shards

[react-sizebot]

Comparing: 0962f68...6d92509

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.js	=	6.68 kB	6.68 kB	=	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	517.29 kB	517.29 kB	=	92.26 kB	92.26 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	617.58 kB	617.58 kB	=	109.52 kB	109.52 kB
facebook-www/ReactDOM-prod.classic.js	=	653.67 kB	653.67 kB	=	115.18 kB	115.18 kB
facebook-www/ReactDOM-prod.modern.js	=	643.95 kB	643.95 kB	=	113.59 kB	113.59 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 6d92509