Fix class inherit from null

[HalidOdat]

Fixes class inheritance from null, which was causing this test262 test to fail: test/language/statements/class/subclass/class-definition-null-proto-this.js

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	95,574	95,574	0
Passed	75,165	75,167	+2
Ignored	19,494	19,494	0
Failed	915	913	-2
Panics	0	0	0
Conformance	78.65%	78.65%	+0.00%

Fixed tests (2):

test/language/statements/class/subclass/class-definition-null-proto-this.js [strict mode] (previously Failed)
test/language/statements/class/subclass/class-definition-null-proto-this.js (previously Failed)

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (25c120b) 49.80% compared to head (721e5db) 49.79%.
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3312      +/-   ##
==========================================
- Coverage   49.80%   49.79%   -0.01%     
==========================================
  Files         441      441              
  Lines       43078    43083       +5     
==========================================
- Hits        21456    21455       -1     
- Misses      21622    21628       +6     

Files	Coverage Δ
boa_engine/src/vm/opcode/mod.rs	7.03% <ø> (ø)
boa_engine/src/vm/opcode/set/class_prototype.rs	93.93% <ø> (ø)
boa_engine/src/vm/opcode/push/class/mod.rs	74.07% <84.21%> (+10.07%)	⬆️

... and 15 files with indirect coverage changes

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[jedel1043]

Nice catch!