Fix data race in BufferedRuntimeExecutor

[lexs]

Summary:
isBufferingEnabled_ can be read (by design) from multiple threads, but
it's not atomic. Make it so.

Differential Revision: D59907026

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D59907026

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	21,354,853	+22
android	hermes	armeabi-v7a	n/a	--
android	hermes	x86	n/a	--
android	hermes	x86_64	n/a	--
android	jsc	arm64-v8a	24,549,989	+6
android	jsc	armeabi-v7a	n/a	--
android	jsc	x86	n/a	--
android	jsc	x86_64	n/a	--

Base commit: c82edec
Branch: main

[facebook-github-bot]

This pull request has been merged in a37534e.

[react-native-bot]

This pull request was successfully merged by Alexander Blom in a37534e

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