Add transparency support to all image types (#4600)

script/ci-custom.py

@@ -66,6 +66,7 @@ file_types = (
     ".txt",
     ".ico",
     ".svg",
+    ".png",
     ".py",
     ".html",
     ".js",
@@ -80,7 +81,7 @@ file_types = (
     "",
 )
 cpp_include = ("*.h", "*.c", "*.cpp", "*.tcc")
-ignore_types = (".ico", ".woff", ".woff2", "")
+ignore_types = (".ico", ".png", ".woff", ".woff2", "")
 
 LINT_FILE_CHECKS = []
 LINT_CONTENT_CHECKS = []