more stable metrics sdk tests

[cijothomas]

Follow up to #1766, we can make tests more predictable!

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 71.6%. Comparing base (348ec9e) to head (5b2b5bd).
Report is 36 commits behind head on main.

Files	Patch %	Lines
opentelemetry-sdk/src/metrics/mod.rs	85.7%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1768     +/-   ##
=======================================
+ Coverage   71.0%   71.6%   +0.6%     
=======================================
  Files        135     136      +1     
  Lines      20751   20857    +106     
=======================================
+ Hits       14746   14951    +205     
+ Misses      6005    5906     -99     

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