Displayed self-confidence becomes an asset when applying for a job. You may find yourself competing with many others with the same credentials that you do. Self-confidence may very well make the difference between getting the job and not getting it.
Public speaking is much more than standing before a group and speaking. It also involves listening to your audience, processing what they say and then being able to interact with them. As a teacher, you will be a role model, helping to mold young minds. Far better to inspire them with your self-confidence rather than your fear.
So yes, Toastmasters can be beneficial to you, if you work within the program. You can’t do it by osmosis. It takes work and a strategic plan to continually raise the bar so that you are growing.
From a strategic perspective, it is probably better to start your personal journey in Toastmasters before going to university or college for your teaching. I would expect that you will likely too busy to focus on many other activities while you are in school.