Only alert on context.Background in go files

_support/detect-context.sh

 #!/bin/sh
 
-git grep 'context.\(Background\|TODO\)' | grep -v -e '^[^:]*_test.go:' -e '^vendor/' -e '^_support/' | awk '{
+git grep 'context.\(Background\|TODO\)' | \
+    grep -v -e '^[^:]*_test\.go:' -e '^vendor/' -e '^_support/' | \
+    grep -e '^[^:]*\.go' | \
+    awk '{
   print "Found disallowed use of context.Background or TODO"
   print
   exit 1