fix(#144): read `sourceType` w/ both flat/legacy config #453

Job	Run time
Lint and Test with Node.js 18 and ESLint 8.56 on macos-latest	1m 26s
Lint and Test with Node.js 18 and ESLint 8 on macos-latest	1m 23s
Lint and Test with Node.js 18 and ESLint 9 on macos-latest	1m 21s
Lint and Test with Node.js 20 and ESLint 8.56 on macos-latest	1m 47s
Lint and Test with Node.js 20 and ESLint 8 on macos-latest	1m 16s
Lint and Test with Node.js 20 and ESLint 9 on macos-latest	1s
Lint and Test with Node.js 22 and ESLint 8.56 on macos-latest	1s
Lint and Test with Node.js 22 and ESLint 8 on macos-latest	1s
Lint and Test with Node.js 22 and ESLint 9 on macos-latest	1s
Lint and Test with Node.js 18 and ESLint 8.56 on ubuntu-latest	1m 24s
Lint and Test with Node.js 18 and ESLint 8 on ubuntu-latest	1m 24s
Lint and Test with Node.js 18 and ESLint 9 on ubuntu-latest	1m 28s
Lint and Test with Node.js 20 and ESLint 8.56 on ubuntu-latest	1m 32s
Lint and Test with Node.js 20 and ESLint 8 on ubuntu-latest	1m 29s
Lint and Test with Node.js 20 and ESLint 9 on ubuntu-latest	1m 27s
Lint and Test with Node.js 22 and ESLint 8.56 on ubuntu-latest	1m 22s
Lint and Test with Node.js 22 and ESLint 8 on ubuntu-latest	1m 12s
Lint and Test with Node.js 22 and ESLint 9 on ubuntu-latest	1m 12s
	19m 47s

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