Add libinteraction to .gn check_targets list

libinteraction is used in certain internal builds.

Bug: b/110808839
Change-Id: I51c29bd0033d608413e97029f288de44b89fc441
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1560138
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Luke Halliwell <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649229}

.gn

@@ -287,6 +287,7 @@ check_targets = [
   #"//jingle/*",
 
   "//libassistant/communication/*",
+  "//libinteraction/*",
 
   "//media/*",
   "//mojo/*",