chore: enable forcetypeassert linter, fix issues (#38804)

Enable [`forcetypeassert`](https://github.com/gostaticanalysis/forcetypeassert)
linter to prevent unchecked type assertions. ~650 issues fixed, most
fixes were clean, some use `setting.PanicInDevOrTesting`.

The only behaviour changes are where code would previously send a 500 error
or panic, a 4xx error is now emitted.

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/turnstile/turnstile.go

@@ -20,7 +20,7 @@ import (
 // httpClient returns an HTTP client that honors Gitea's proxy configuration.
 var httpClient = util.OnceValue[*http.Client]{
 	Func: func() *http.Client {
-		transport := http.DefaultTransport.(*http.Transport).Clone()
+		transport := http.DefaultTransport.(*http.Transport).Clone() //nolint:forcetypeassert // Golang stdlib
 		transport.Proxy = proxy.Proxy()
 		return &http.Client{Transport: transport}
 	},