[sdk-metrics] Fix a race condition when a metric is deactivated and re-activated in the same collection cycle

[CodeBlanch]

Fixes #5907

Changes

• Use TryUpdate instead of TryRemove when processing a removed metric so that the lookup dictionary is only modified if a new metric hasn't already been enrolled

Merge requirement checklist

• [X] CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)