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/markup/markdown/transform_list.go

@@ -15,7 +15,7 @@ import (
 )
 
 func (r *HTMLRenderer) renderTaskCheckBoxListItem(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
-	n := node.(*TaskCheckBoxListItem)
+	n := node.(*TaskCheckBoxListItem) //nolint:forcetypeassert // registered for KindTaskCheckBoxListItem only
 	if entering {
 		if n.Attributes() != nil {
 			_, _ = w.WriteString("<li")
@@ -60,7 +60,7 @@ func (g *ASTTransformer) transformList(_ *markup.RenderContext, v *ast.List, rc
 		v.RemoveChildren(v)
 
 		for _, child := range children {
-			listItem := child.(*ast.ListItem)
+			listItem := child.(*ast.ListItem) //nolint:forcetypeassert // a list only holds list items
 			if !child.HasChildren() || !child.FirstChild().HasChildren() {
 				v.AppendChild(v, child)
 				continue