Fix base_ring_type for ClassField

[fingolfin]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 75.94%. Comparing base (cd361f4) to head (ab8304d).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/RCF/class_fields.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1698      +/-   ##
==========================================
+ Coverage   75.89%   75.94%   +0.04%     
==========================================
  Files         362      362              
  Lines      114377   114377              
==========================================
+ Hits        86807    86864      +57     
+ Misses      27570    27513      -57     

Files with missing lines	Coverage Δ
src/RCF/class_fields.jl	57.55% <0.00%> (ø)

... and 29 files with indirect coverage changes