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/graceful/server.go

@@ -7,6 +7,7 @@ package graceful
 
 import (
 	"crypto/tls"
+	"fmt"
 	"net"
 	"os"
 	"strings"
@@ -260,7 +261,11 @@ func (wl *wrappedListener) Accept() (c net.Conn, err error) {
 
 func (wl *wrappedListener) File() (*os.File, error) {
 	// returns a dup(2) - FD_CLOEXEC flag *not* set so the listening socket can be passed to child processes
-	return wl.Listener.(filer).File()
+	lf, ok := wl.Listener.(filer)
+	if !ok {
+		return nil, fmt.Errorf("listener %T does not provide a File", wl.Listener)
+	}
+	return lf.File()
 }
 
 type wrappedConn struct {