fix: An extra test that is still calling old JsonStreamWriter append

[yirutang]

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Fixes #<issue_number_goes_here> ☕️

[codecov]

Codecov Report

Merging #760 (5868a3a) into master (0988105) will increase coverage by 0.01%.
The diff coverage is 82.50%.

@@             Coverage Diff              @@
##             master     #760      +/-   ##
============================================
+ Coverage     80.84%   80.85%   +0.01%     
- Complexity      983      992       +9     
============================================
  Files            73       74       +1     
  Lines          5283     5333      +50     
  Branches        404      412       +8     
============================================
+ Hits           4271     4312      +41     
- Misses          843      848       +5     
- Partials        169      173       +4     

Impacted Files	Coverage Δ	Complexity Δ
...oud/bigquery/storage/v1beta2/JsonStreamWriter.java	78.99% <79.16%> (+1.11%)	15.00 <2.00> (+2.00)
...e/cloud/bigquery/storage/v1beta2/StreamWriter.java	85.01% <82.60%> (-0.08%)	38.00 <2.00> (+1.00)	⬇️
...uery/storage/v1beta2/BQV2ToBQStorageConverter.java	84.84% <84.84%> (ø)	6.00 <6.00> (?)
.../cloud/bigquery/storage/v1alpha2/StreamWriter.java	83.87% <0.00%> (-0.44%)	37.00% <0.00%> (ø%)

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