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>

routers/web/repo/setting/deploy_key.go

@@ -34,7 +34,7 @@ func DeployKeys(ctx *context.Context) {
 
 // DeployKeysPost response for adding a deploy key of a repository
 func DeployKeysPost(ctx *context.Context) {
-	form := web.GetForm(ctx).(*forms.AddKeyForm)
+	form := web.GetForm[*forms.AddKeyForm](ctx)
 	ctx.Data["Title"] = ctx.Tr("repo.settings.deploy_keys")
 	ctx.Data["PageIsSettingsKeys"] = true
 	ctx.Data["DisableSSH"] = setting.SSH.Disabled