lint: fix quoting style everywhere

BUG=chromium:990019
TEST=`cros lint` is clean & CQ passes

Change-Id: I012966d34a45a01b3a940414b24316aee4ffe8af
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1731476
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Will Bradley <wbbradley@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/pushimage.py b/scripts/pushimage.py
index f6192a1..ca9385d 100644
--- a/scripts/pushimage.py
+++ b/scripts/pushimage.py
@@ -387,7 +387,7 @@
 
   # These variables are defined outside the loop so that the nested functions
   # below can access them without 'cell-var-from-loop' linter warning.
-  dst_path = ""
+  dst_path = ''
   files_to_sign = []
   for channel in channels:
     logging.debug('\n\n#### CHANNEL: %s ####\n', channel)