pnpm-sync-lib should support pnpm v9

[fzxen]

I am trying to enable @microsoft/rush to support pnpm v9, and I found that after enabling the subspace feature, pnpm-sync-lib will encounter compatibility errors.

error log:
ERROR: pnpm-sync: The pnpm version is not supported; pnpm-sync requires pnpm version 8.x

pnpm-sync/packages/pnpm-sync-lib/src/pnpmSyncPrepare.ts

Lines 103 to 114 in 68a2760

	if (!pnpmVersion || !pnpmVersion.startsWith('8')) {
	logMessageCallback({
	message: `The pnpm version is not supported; pnpm-sync requires pnpm version 8.x`,
	messageKind: LogMessageKind.ERROR,
	details: {
	messageIdentifier: LogMessageIdentifier.PREPARE_ERROR_UNSUPPORTED_PNPM_VERSION,
	lockfilePath,
	pnpmVersion: pnpmVersion
	}
	});
	return;
	}