Add fetch wrappers, ignore network errors in actions view (#26985)

1. Introduce lightweight `fetch` wrapper functions that automatically
sets csfr token, content-type and use it in `RepoActionView.vue`.
2. Fix a specific issue on `RepoActionView.vue` where a fetch network
error is shortly visible during page reload sometimes. It can be
reproduced by F5-in in quick succession on the actions view page and was
also producing a red error box on the page.

Once approved, we can replace all current `fetch` uses in UI with this
in another PR.

---------

Co-authored-by: Giteabot <teabot@gitea.io>

docs/content/contributing/guidelines-frontend.en-us.md

@@ -92,6 +92,12 @@ it's recommended to use `const _promise = asyncFoo()` to tell readers
 that this is done by purpose, we want to call the async function and ignore the Promise.
 Some lint rules and IDEs also have warnings if the returned Promise is not handled.
 
+### Fetching data
+
+To fetch data, use the wrapper functions `GET`, `POST` etc. from `modules/fetch.js`. They
+accept a `data` option for the content, will automatically set CSFR token and return a
+Promise for a [Response](https://developer.mozilla.org/en-US/docs/Web/API/Response).
+
 ### HTML Attributes and `dataset`
 
 The usage of `dataset` is forbidden, its camel-casing behaviour makes it hard to grep for attributes.