fix(askar): in memory wallet creation

[genaris]

Quick fix to allow the creation of an in-memory wallet (for test purposes). Previously, the parameter was supported but, due to a particular error thrown by @hyperledger/askar-shared it was not working.

[codecov-commenter]

Codecov Report

Merging #1498 (c026f7d) into main (04a8058) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1498      +/-   ##
==========================================
+ Coverage   85.79%   85.83%   +0.03%     
==========================================
  Files         943      943              
  Lines       22588    22608      +20     
  Branches     3915     3919       +4     
==========================================
+ Hits        19380    19406      +26     
+ Misses       3027     3021       -6     
  Partials      181      181              

Impacted Files	Coverage Δ
packages/askar/src/wallet/AskarWallet.ts	66.35% <100.00%> (+0.31%)	⬆️
packages/askar/tests/helpers.ts	97.61% <100.00%> (+1.61%)	⬆️

... and 4 files with indirect coverage changes