fix release staging

[Polber]

The release is failing to stage because for some reason Cloud Build commands always return non-zero exit code when run as java subprocess (even when successful). This PR refactors the recently added cloud build command from throwing an exception to logging a WARN.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 45.26%. Comparing base (ba67089) to head (8920ff9).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1992      +/-   ##
============================================
- Coverage     45.27%   45.26%   -0.01%     
+ Complexity     3632     3630       -2     
============================================
  Files           836      836              
  Lines         49872    49872              
  Branches       5253     5253              
============================================
- Hits          22579    22575       -4     
- Misses        25618    25622       +4     
  Partials       1675     1675              

Components	Coverage Δ
spanner-templates	66.61% <ø> (-0.01%)	⬇️
spanner-import-export	64.16% <ø> (-0.03%)	⬇️
spanner-live-forward-migration	75.86% <ø> (ø)
spanner-live-reverse-replication	76.63% <ø> (ø)
spanner-bulk-migration	86.42% <ø> (ø)

see 2 files with indirect coverage changes