runtime-sdk/core: do not enforce batch gas limit for CheckTx

[ptrus]

With oasisprotocol/oasis-core#4131 oasis-core will be scheduling CheckTx batches. The runtime scheduler cannot enforce batch-limits for non-checked transactions, therefore the runtime should not enforce these either.

Other batch limits (emitted messages, batch size) are already not enforced for check-tx batches.

[codecov]

Codecov Report

Merging #290 (abc99aa) into main (6dad5ed) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #290      +/-   ##
==========================================
+ Coverage   70.70%   70.78%   +0.07%     
==========================================
  Files          57       57              
  Lines        3455     3464       +9     
==========================================
+ Hits         2443     2452       +9     
  Misses        992      992              
  Partials       20       20              

Impacted Files	Coverage Δ
runtime-sdk/src/modules/core/mod.rs	80.58% <100.00%> (+0.38%)	⬆️
runtime-sdk/src/modules/core/test.rs	95.17% <100.00%> (+0.17%)	⬆️
runtime-sdk/src/testing/mock.rs	90.32% <100.00%> (+0.66%)	⬆️

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