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>

models/db/error.go

@@ -14,12 +14,6 @@ type ErrCancelled struct {
 	Message string
 }
 
-// IsErrCancelled checks if an error is a ErrCancelled.
-func IsErrCancelled(err error) bool {
-	_, ok := err.(ErrCancelled)
-	return ok
-}
-
 func (err ErrCancelled) Error() string {
 	return "Cancelled: " + err.Message
 }