Fix _fe_analyzer_shared sdk constraint
Fix _fe_analyzer_shared sdk constraint

This was causing issues as I believe 2.12 takes precedent over pre-releases with -x.

Change-Id: I4ca2433e266998782cdf3f677dbefd3149a1a054
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175940
Reviewed-by: Konstantin Shcheglov <09e4d7516628963212bf4aace2f97603d2b706e4@google.com>
Commit-Queue: Konstantin Shcheglov <09e4d7516628963212bf4aace2f97603d2b706e4@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk