chore: update eslint, enable more rules and fix their findings (#39438)

Update eslint and its plugins, enable more rules and fix their findings:

1. `unicorn/no-unsafe-string-replacement` found that uploading a file
whose name contains `$&` inserted a broken markdown link, because
`String#replace` expands such patterns in the replacement string
2. `@typescript-eslint/require-await` removes `async` from functions
that never await
3. Plugin rules not covered by a preset are now listed explicitly

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Co-authored-by: bircni <bircni@icloud.com>

web_src/js/markup/render-iframe.ts

@@ -42,7 +42,7 @@ function getRealBackgroundColor(el: HTMLElement) {
   return '';
 }
 
-export async function initExternalRenderIframe(iframe: HTMLIFrameElement) {
+export function initExternalRenderIframe(iframe: HTMLIFrameElement) {
   const iframeSrcUrl = iframe.getAttribute('data-src')!;
   if (!iframe.id) iframe.id = generateElemId('gitea-iframe-');