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>

tests/integration/oauth_avatar_test.go

@@ -39,7 +39,9 @@ func TestOAuth2AvatarFromPicture(t *testing.T) {
 	})
 	authSource, err := auth_model.GetActiveOAuth2SourceByAuthName(t.Context(), "test-oidc-avatar")
 	require.NoError(t, err)
-	providerName := authSource.Cfg.(*oauth2.Source).Provider
+	oauth2Source, ok := authSource.Cfg.(*oauth2.Source)
+	require.True(t, ok)
+	providerName := oauth2Source.Provider
 
 	t.Run("AutoRegister", func(t *testing.T) {
 		defer test.MockVariableValue(&setting.OAuth2Client.Username, "")()