Tests wrongly expecting type arguments to be modified by NNBD_TOP_MERGE

[crelier]

The following tests wrongly expect class type arguments to be modified by NNBD_TOP_MERGE:

LanguageFeatures/nnbd/overriding/override_checking_A06_t012
LanguageFeatures/nnbd/overriding/override_checking_A06_t026
LanguageFeatures/nnbd/overriding/override_checking_A06_t029
LanguageFeatures/nnbd/overriding/override_checking_A06_t043
LanguageFeatures/nnbd/overriding/override_checking_A06_t047
LanguageFeatures/nnbd/overriding/override_checking_A06_t052
LanguageFeatures/nnbd/overriding/override_checking_A06_t054
LanguageFeatures/nnbd/overriding/override_checking_A06_t071
LanguageFeatures/nnbd/overriding/override_checking_A06_t072
LanguageFeatures/nnbd/overriding/override_checking_A06_t085
LanguageFeatures/nnbd/overriding/override_checking_A06_t100
LanguageFeatures/nnbd/overriding/override_checking_A06_t115
LanguageFeatures/nnbd/overriding/override_checking_A06_t121
LanguageFeatures/nnbd/overriding/override_checking_A06_t122
LanguageFeatures/nnbd/overriding/override_checking_A06_t124
LanguageFeatures/nnbd/overriding/override_checking_A06_t130
LanguageFeatures/nnbd/overriding/override_checking_A06_t147
LanguageFeatures/nnbd/overriding/override_checking_A06_t148
LanguageFeatures/nnbd/overriding/override_checking_A06_t154
LanguageFeatures/nnbd/overriding/override_checking_A06_t156
LanguageFeatures/nnbd/overriding/override_checking_A06_t159

See also #623

[iarkh]

It's a duplicate of the Issues #619, #623 which already were fixed yesterday.