Add avif image file support (#32508)

Most modern browsers support it now

` Update ALLOWED_TYPES #96 ` https://gitea.com/gitea/docs/pulls/96

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Co-authored-by: silverwind <me@silverwind.io>

web_src/js/utils.test.ts

@@ -118,7 +118,7 @@ test('encodeURLEncodedBase64, decodeURLEncodedBase64', () => {
 });
 
 test('file detection', () => {
-  for (const name of ['a.jpg', '/a.jpeg', '.file.png', '.webp', 'file.svg']) {
+  for (const name of ['a.avif', 'a.jpg', '/a.jpeg', '.file.png', '.webp', 'file.svg']) {
     expect(isImageFile({name})).toBeTruthy();
   }
   for (const name of ['', 'a.jpg.x', '/path.png/x', 'webp']) {