added it-integration-test-parallelism and set this to 6

[liferoad]

also switched to us-west2 for the create job for releasing.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 49.63%. Comparing base (dcd6be2) to head (caab89b).
Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2483      +/-   ##
============================================
- Coverage     49.64%   49.63%   -0.01%     
- Complexity     4806     4807       +1     
============================================
  Files           941      941              
  Lines         57683    57683              
  Branches       6233     6233              
============================================
- Hits          28634    28633       -1     
- Misses        27007    27010       +3     
+ Partials       2042     2040       -2     

Components	Coverage Δ
spanner-templates	69.95% <ø> (+<0.01%)	⬆️
spanner-import-export	68.63% <ø> (+0.02%)	⬆️
spanner-live-forward-migration	78.77% <ø> (ø)
spanner-live-reverse-replication	77.36% <ø> (ø)
spanner-bulk-migration	87.89% <ø> (ø)

see 2 files with indirect coverage changes

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