[ci] Fix missing values during manual workflow dispatch

[poteto]

Stack from ghstack (oldest at bottom):

• [ez] Update deprecated action #31047
• [ez] Make commit sha clickable for fbsource #31046
• -> [ci] Fix missing values during manual workflow dispatch #31045

It seems like the github.event.workflow_run payload is only populated
for non manual runs of the workflow, so this would crash the manual
dispatch

Test plan: https://github.com/facebook/react/actions/runs/11017512571
completes

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
react-compiler-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Sep 26, 2024 2:09pm

[react-sizebot]

Comparing: db320ea...e6a2463

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	+0.05%	1.82 kB	1.82 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	507.20 kB	507.20 kB	=	90.80 kB	90.80 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	+0.05%	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	512.13 kB	512.13 kB	=	91.52 kB	91.52 kB
facebook-www/ReactDOM-prod.classic.js	=	603.73 kB	603.73 kB	=	106.83 kB	106.84 kB
facebook-www/ReactDOM-prod.modern.js	=	579.95 kB	579.95 kB	=	102.92 kB	102.92 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 4504c0c