Force python3 to be used in build

Bug:  none
Change-Id: I17905932cd7b15ec30ab8283c114bf3553c64daf
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2828111
Reviewed-by: Tim van der Lippe <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Commit-Queue: Philip Pfaffe <[email protected]>

Author: pfaffe

.gn

@@ -15,5 +15,7 @@ buildconfig = "//build_overrides/BUILDCONFIG.gn"
 # "gn check" or "gn gen --check".
 check_targets = [ "*" ]
 
+script_executable = "python3"
+
 default_args = {
 }