Increase parallelism for drone apps tests [test apps][skip ui]

[uponthesun]

Re-ran this a few times to see if it greatly increased flakiness - at parallelism=2 it succeeded all 5 times.

We can go back down to 1 if we observe issues.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (staging@2239281). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             staging   #30304   +/-   ##
==========================================
  Coverage           ?   72.14%           
==========================================
  Files              ?     1372           
  Lines              ?    84637           
  Branches           ?     3424           
==========================================
  Hits               ?    61063           
  Misses             ?    20334           
  Partials           ?     3240

Flag	Coverage Δ
#integration	55.81% <ø> (?)
#storybook	56.6% <ø> (?)
#unit	58.06% <ø> (?)

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