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/goldmark.go

@@ -43,8 +43,8 @@ func (g *ASTTransformer) applyElementDir(n ast.Node) {
 // Transform transforms the given AST tree.
 func (g *ASTTransformer) Transform(node *ast.Document, reader text.Reader, pc parser.Context) {
 	firstChild := node.FirstChild()
-	ctx := pc.Get(renderContextKey).(*markup.RenderContext)
-	rc := pc.Get(renderConfigKey).(*RenderConfig)
+	ctx := pc.Get(renderContextKey).(*markup.RenderContext) //nolint:forcetypeassert // the renderer always seeds this key before parsing
+	rc := pc.Get(renderConfigKey).(*RenderConfig)           //nolint:forcetypeassert // the renderer always seeds this key before parsing
 
 	tocMode := ""
 	if rc.yamlNode != nil {
@@ -150,9 +150,7 @@ func (r *HTMLRenderer) renderCodeBlock(w util.BufWriter, source []byte, n ast.No
 }
 
 func (r *HTMLRenderer) renderDocument(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
-	n := node.(*ast.Document)
-
-	if val, has := n.AttributeString("lang"); has {
+	if val, has := node.AttributeString("lang"); has {
 		var err error
 		if entering {
 			_, err = w.WriteString("<div")
@@ -212,7 +210,7 @@ func (r *HTMLRenderer) renderRawHTML(w util.BufWriter, source []byte, node ast.N
 	if !entering {
 		return ast.WalkContinue, nil
 	}
-	n := node.(*RawHTML)
+	n := node.(*RawHTML) //nolint:forcetypeassert // registered for KindRawHTML only
 	_, err := w.WriteString(string(r.renderInternal.ProtectSafeAttrs(n.rawHTML)))
 	if err != nil {
 		return ast.WalkStop, err