CheckCompilerFlag: Fix regression in locale environment preservation

Fix a typo from commit 660e0d80 (internal/CheckCompilerFlag: rely on
common configuration, 2022-01-12, v3.23.0-rc1~124^2~1) that caused
locale environment variables to not be restored after they are set
during the check.
38 jobs for !7153 with CheckCompilerFlag-restore-env in 29 minutes and 4 seconds (queued for 4 seconds)
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