lint: Add a few strings to capitalization linter.

My hope is that we'll be able to eliminate these strings from the UI
altogether soon, but this is needed to keep CI passing for now.

tools/lib/capitalization.py

@@ -66,6 +66,8 @@ IGNORED_PHRASES = [
     r"images",
     r"enabled",
     r"disabled",
+    r"be",
+    r"^not be$",
 
     # Fragments of larger strings
     (r'your subscriptions on your Streams page'),