Updated checked-in SDK to 7c64e31

Includes fix for #55212 which is
causing build breakages.

Change-Id: Ie665b71970fd8ff2103f6fe5d7d1411ac6f8adc0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/358540
Reviewed-by: Alexander Thomas <[email protected]>
Reviewed-by: Alexander Markov <[email protected]>

Author: bkonyi

DEPS

@@ -50,7 +50,7 @@ vars = {
   # Checked-in SDK version. The checked-in SDK is a Dart SDK distribution
   # in a cipd package used to run Dart scripts in the build and test
   # infrastructure, which is automatically built on the release commits.
-  "sdk_tag": "version:3.4.0-108.0.dev",
+  "sdk_tag": "git_revision:7c64e31f4c3eaa0bcfd29ce40459b74cf20a806d",
 
   # co19 is a cipd package automatically generated for each co19 commit.
   # Use tests/co19/update.sh to update this hash.