fix: Sanitize value in metrics

[bitsandfoxes]

Fixes getsentry/symbol-collector#175

[bruno-garcia]

if we had tests we wouldn't have had this bug in prod, can u add a test?

[bitsandfoxes]

if we had tests we wouldn't have had this bug in prod, can u add a test?

Of course!

[jamescrosswell]

if we had tests we wouldn't have had this bug in prod, can u add a test?

We probably need tests more generally for the metrics capability. We intentionally didn't do much testing just to put a POC together but I think we need to circle back to this:

• Improve test coverage for Metrics API #3066

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d3f2f7a) 76.42% compared to head (8d0c9d0) 75.39%.
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3065      +/-   ##
==========================================
- Coverage   76.42%   75.39%   -1.03%     
==========================================
  Files         351      351              
  Lines       13263    13259       -4     
  Branches     2646     2644       -2     
==========================================
- Hits        10136     9997     -139     
- Misses       2450     2588     +138     
+ Partials      677      674       -3     

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