[compiler] Check if current branch is main

[poteto]

Stack from ghstack (oldest at bottom):

• -> [compiler] Check if current branch is main #29083
• [compiler] Various fixes for publishing script #29082

This script needs to run from main since it commits version bumps for
packages, and those need to point to publicly available hashes. So,
throw an error if we're not already on main.

[react-sizebot]

Comparing: cf7d895...6ca227b

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	=	6.66 kB	6.66 kB	=	1.82 kB	1.82 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	495.01 kB	495.01 kB	=	88.68 kB	88.68 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.67 kB	6.67 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	499.81 kB	499.81 kB	=	89.36 kB	89.36 kB
facebook-www/ReactDOM-prod.classic.js	=	592.16 kB	592.16 kB	=	104.15 kB	104.15 kB
facebook-www/ReactDOM-prod.modern.js	=	568.39 kB	568.39 kB	=	100.55 kB	100.55 kB
test_utils/ReactAllWarnings.js	Deleted	64.26 kB	0.00 kB	Deleted	16.02 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	64.26 kB	0.00 kB	Deleted	16.02 kB	0.00 kB

Generated by 🚫 dangerJS against 6ca227b

[josephsavona]

Would be good to also check that there are no local modifications

[poteto]

Would be good to also check that there are no local modifications

Fixed, thanks!