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/math/inline_renderer.go

@@ -30,7 +30,7 @@ func (r *InlineRenderer) renderInline(w util.BufWriter, source []byte, n ast.Nod
 	if entering {
 		_, _ = w.WriteString(string(r.renderInternal.ProtectSafeAttrs(`<code class="language-math">`)))
 		for c := n.FirstChild(); c != nil; c = c.NextSibling() {
-			segment := c.(*ast.Text).Segment
+			segment := c.(*ast.Text).Segment //nolint:forcetypeassert // an inline math node only holds text children
 			value := util.EscapeHTML(segment.Value(source))
 			if bytes.HasSuffix(value, []byte("\n")) {
 				_, _ = w.Write(value[:len(value)-1])