test: add a test for selecting an array of structs

[olavloite]

Test to ensure the error in googleapis/java-spanner-jdbc#444 is not present in the Java client library.

[codecov]

Codecov Report

Merging #1108 (c8926f6) into master (ce095f7) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1108      +/-   ##
============================================
- Coverage     84.91%   84.90%   -0.01%     
+ Complexity     2725     2723       -2     
============================================
  Files           156      156              
  Lines         14410    14410              
  Branches       1379     1379              
============================================
- Hits          12236    12235       -1     
  Misses         1607     1607              
- Partials        567      568       +1     

Impacted Files	Coverage Δ	Complexity Δ
...ud/spanner/SessionPoolAsyncTransactionManager.java	85.03% <0.00%> (-1.58%)	13.00% <0.00%> (-2.00%)
...ain/java/com/google/cloud/spanner/SessionPool.java	88.82% <0.00%> (ø)	73.00% <0.00%> (-1.00%)
...m/google/cloud/spanner/connection/SpannerPool.java	87.70% <0.00%> (+0.53%)	33.00% <0.00%> (ø%)

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