[ci] Only install chromium for flight fixtures

[poteto]

I noticed we only use chromium in fixtures/flight, so let's specifically only install that browser in ci.

[react-sizebot]

Comparing: 4b3728f05efbab9624e981339d8a0992a58f9a41...1a48c738ebe1465996971b74b116a431bfd45f8a

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	=	514.64 kB	514.64 kB	=	91.76 kB	91.76 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	=	557.67 kB	557.67 kB	=	99.01 kB	99.01 kB
facebook-www/ReactDOM-prod.classic.js	=	596.61 kB	596.61 kB	=	104.90 kB	104.89 kB
facebook-www/ReactDOM-prod.modern.js	=	587.04 kB	587.04 kB	=	103.36 kB	103.36 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

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