ci: Only run runtime tests when testing SGX

[kostko]

Fixes #3034

[codecov]

Codecov Report

Merging #3051 into master will increase coverage by 0.24%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3051      +/-   ##
==========================================
+ Coverage   68.32%   68.57%   +0.24%     
==========================================
  Files         371      371              
  Lines       36424    36424              
==========================================
+ Hits        24888    24979      +91     
+ Misses       8323     8243      -80     
+ Partials     3213     3202      -11     

Impacted Files	Coverage Δ
go/keymanager/api/policy_sgx.go	33.33% <0.00%> (-13.34%)	⬇️
...consensus/tendermint/apps/keymanager/keymanager.go	66.29% <0.00%> (-3.38%)	⬇️
...nsensus/tendermint/apps/keymanager/transactions.go	50.00% <0.00%> (-2.95%)	⬇️
go/storage/api/root_cache.go	70.11% <0.00%> (-2.30%)	⬇️
go/consensus/tendermint/roothash/roothash.go	66.47% <0.00%> (-2.03%)	⬇️
go/oasis-node/cmd/keymanager/keymanager.go	48.88% <0.00%> (-1.95%)	⬇️
...consensus/tendermint/apps/scheduler/state/state.go	71.15% <0.00%> (-1.93%)	⬇️
...consensus/tendermint/apps/roothash/transactions.go	61.32% <0.00%> (-1.89%)	⬇️
go/storage/database/database.go	70.58% <0.00%> (-1.69%)	⬇️
go/roothash/api/commitment/pool.go	70.54% <0.00%> (-1.63%)	⬇️
... and 28 more

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