SetTheme() behaves is not fully effective for widget.Form

[BabySid]

Describe the bug:

I have the same problem #842
When I SetTheme(), I found that the text color of FormItem did not refresh.
I checked my code and found that there should be no misuse in use. I searched the issue and found similar problems as above.

To Reproduce:

Steps to reproduce the behaviour:

1. Run the code below

Screenshots:

When Theme is Light, it is normal.

When Theme switch to Dark, I hope the text of FormItems is white, but it's actually black.

Example code:

package main

import (
	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/theme"
	"fyne.io/fyne/v2/widget"
)

func main() {
	myApp := app.New()
	myWindow := myApp.NewWindow("Rick&Morty")
	myWindow.SetMainMenu(fyne.NewMainMenu(fyne.NewMenu("Menu",
		fyne.NewMenuItem("Dark Theme", func() { myApp.Settings().SetTheme(theme.DarkTheme()) }),
		fyne.NewMenuItem("Light Theme", func() { myApp.Settings().SetTheme(theme.LightTheme()) }),
	)))

	form := widget.NewForm()
	form.Append("ID", widget.NewLabel("Character's Name"))
	form.Append("be", widget.NewLabel("bebe"))

	myWindow.SetContent(form)
	myWindow.ShowAndRun()
}

Device (please complete the following information):

• OS: Windows10
• Version: 19044
• Go version: 1.17.5
• Fyne version: 2.1.3

[andydotxyz]

Thanks for reporting this, confirmed

[andydotxyz]

Resolved for next release (v2.1.4 or v2.2.0)