Add few shot subset for mSuperb multilingual setting

[guapaQAQ]

Select 5 sentences for the reserved 20 langs

[codecov]

Codecov Report

Merging #4923 (7950964) into master (b041c9d) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4923   +/-   ##
=======================================
  Coverage   76.57%   76.58%           
=======================================
  Files         603      603           
  Lines       53739    53739           
=======================================
+ Hits        41150    41154    +4     
+ Misses      12589    12585    -4     

Flag	Coverage Δ
test_integration_espnet1	66.33% <ø> (ø)
test_integration_espnet2	47.59% <ø> (+0.02%)	⬆️
test_python	66.46% <ø> (ø)
test_utils	23.35% <ø> (ø)

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Impacted Files	Coverage Δ
espnet2/train/trainer.py	77.33% <0.00%> (+0.93%)	⬆️

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