Use urlsafe_b64decode to properly handle URL-encoded JWTs

[fbeutel]

What kind of change does this PR introduce?

Bug fix

What is the current behavior?

When set_session() is called with a base64URL encoded JWT (instead of normal base64 encoding), it fails. Giving it a normally encoded JWT also fails, because the request later uses the access_token as passed here and it requires base64URL encoding.

What is the new behavior?

By using urlsafe_b64decode, base64URL encoded JWTs now work properly

Additional context

none

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (708859c) 45.68% compared to head (0034af1) 45.68%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #352   +/-   ##
=======================================
  Coverage   45.68%   45.68%           
=======================================
  Files          23       23           
  Lines        1902     1902           
=======================================
  Hits          869      869           
  Misses       1033     1033           

Files	Coverage Δ
gotrue/__init__.py	100.00% <100.00%> (ø)
gotrue/helpers.py	71.87% <50.00%> (ø)

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[J0]

Thanks for the contribution!