Codify spaces in .yml files

.editorconfig

@@ -18,6 +18,9 @@ max_line_length = off
 indent_size = 4
 indent_style = space
 
+[*.yml]
+indent_style = space
+
 # Tests don't get a line width restriction.  It's still a good idea to follow
 # the 79 character rule, but in the interests of clarity, tests often need to
 # violate it.