Auto merge of #8293 - simartin:issue_8113, r=jdm

Issue #8113: Support file, about and data schemes as form action.

Fix https://github.com/servo/servo/issues/8113 by supporting those schemes as form action and unit test the "about:blank" case

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components/script/dom/htmlformelement.rs

@@ -209,7 +209,8 @@ impl HTMLFormElement {
                 load_data.data = Some(parsed_data.into_bytes());
             },
             // https://html.spec.whatwg.org/multipage/#submit-get-action
-            ("ftp", _) | ("javascript", _) | ("data", FormMethod::FormGet) => (),
+            ("file", _) | ("about", _) | ("data", FormMethod::FormGet) |
+            ("ftp", _) | ("javascript", _) => (),
             _ => return // Unimplemented (data and mailto)
         }