avm2: Allow null ratios is Graphics gradient APIs #26493

Job	Run time
Paths filter	7s
Build for browser tests	2m 2s
Test Node.js 20 / ubuntu-24.04	3m 53s
Test in ${{ matrix.browser }}	0s
Test Node.js ${{ matrix.node_version }} / ${{ matrix.os }}	0s
Test Node.js 20 / windows-latest	4m 50s
Test Node.js 22 / ubuntu-24.04	3m 53s
Test Node.js 22 / windows-latest	5m 56s
Test in chrome	1m 43s
Test in firefox	2m 52s
Test in edge	2m 28s
	27m 44s

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