Fix runtime return type backward compatibility

[upgle]

Description

Some downstream runtimes may not support the array return type.
(This also happens when using a legacy action loop base.)

In this case, test case will fail and you will be inconvenient for maintaining.
I think it is should be preserved backward compatibility.

Related issue and scope

#5290

My changes affect the following components

• Tests

Types of changes

• Bug fix (generally a non-breaking change which closes an issue).
• Enhancement or new feature (adds new functionality).
• Breaking change (a bug fix or enhancement which changes existing behavior).

Checklist:

• I signed an Apache CLA.
• I reviewed the style guides and followed the recommendations (Travis CI will check :).
• I added tests to cover my changes.
• My changes require further changes to the documentation.
• I updated the documentation where necessary.

[ningyougang]

LGTM

[codecov-commenter]

Codecov Report

Merging #5306 (e74dadd) into master (2683ed1) will increase coverage by 4.70%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5306      +/-   ##
==========================================
+ Coverage   71.46%   76.16%   +4.70%     
==========================================
  Files         238      238              
  Lines       14183    14178       -5     
  Branches      574      579       +5     
==========================================
+ Hits        10136    10799     +663     
+ Misses       4047     3379     -668     

Impacted Files	Coverage Δ
...core/database/cosmosdb/RxObservableImplicits.scala	0.00% <0.00%> (-100.00%)	⬇️
...ore/database/cosmosdb/cache/CacheInvalidator.scala	0.00% <0.00%> (-100.00%)	⬇️
...e/database/cosmosdb/cache/ChangeFeedConsumer.scala	0.00% <0.00%> (-100.00%)	⬇️
...core/database/cosmosdb/CosmosDBArtifactStore.scala	0.00% <0.00%> (-95.85%)	⬇️
...sk/core/database/cosmosdb/CosmosDBViewMapper.scala	0.00% <0.00%> (-93.90%)	⬇️
...tabase/cosmosdb/cache/CacheInvalidatorConfig.scala	0.00% <0.00%> (-92.31%)	⬇️
...enwhisk/connector/kafka/KamonMetricsReporter.scala	0.00% <0.00%> (-83.34%)	⬇️
...e/database/cosmosdb/cache/KafkaEventProducer.scala	0.00% <0.00%> (-78.58%)	⬇️
...whisk/core/database/cosmosdb/CosmosDBSupport.scala	0.00% <0.00%> (-74.08%)	⬇️
...ore/database/azblob/AzureBlobAttachmentStore.scala	11.53% <0.00%> (-60.58%)	⬇️
... and 33 more

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