Fix browser on Pharo 13

[marschall]

Deal with the removal of RPackage and #classTagForClass being renamed to #tagOf:

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 49.12%. Comparing base (8d8467b) to head (a17d6a6).

Files	Patch %	Lines
...ckageBasedBrowser.class/instance/parentOfClass..st	0.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1424   +/-   ##
=======================================
  Coverage   49.12%   49.12%           
=======================================
  Files        9116     9116           
  Lines       80334    80339    +5     
=======================================
+ Hits        39464    39467    +3     
- Misses      40870    40872    +2     

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