setup: only take svg files as input to build_icons command (#67139)

· Some text editors such as vim perform a local management of their
    swap files. We prevent the command from taking such swap files as
    input while converting svg files to png.

setup.py

@@ -160,6 +160,8 @@ class build_icons(Command):
             for filename in filenames:
                 basename = os.path.splitext(filename)[0]
                 variants = variants_applications
+                if not filename.endswith('.svg'):
+                    continue
                 if filename.startswith('action-'):
                     variants = variants_actions
                 for variant in variants: