fix typo in FullNameExternalAutocomplete default value #1952

Job	Run time
Build on windows-latest for repo global.json	15m 52s
Build on windows-latest for 6.0	12m 47s
Build on windows-latest for 7.0	19m 48s
Build on windows-latest for 8.0	13m 20s
Build on macos-latest for repo global.json	16m 37s
Build on macos-latest for 6.0	18m 40s
Build on macos-latest for 7.0	19m 49s
Build on macos-latest for 8.0	17m 1s
Build on ubuntu-latest for repo global.json	9m 30s
Build on ubuntu-latest for 6.0	14m 16s
Build on ubuntu-latest for 7.0	10m 13s
Build on ubuntu-latest for 8.0	55s
	2h 48m 48s

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