Update opentelemetry-api, ... to 1.21.0

[typelevel-steward]

Updates

• io.opentelemetry:opentelemetry-api
• io.opentelemetry:opentelemetry-sdk
• io.opentelemetry:opentelemetry-sdk-testing

from 1.20.1 to 1.21.0.
GitHub Release Notes - Version Diff

I'll automatically update this PR to resolve conflicts as long as you don't change it yourself.

If you'd like to skip this version, you can just close this PR. If you have any feedback, just mention me in the comments below.

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Adjust future updates

Add this to your .scala-steward.conf file to ignore future updates of this dependency:

updates.ignore = [ { groupId = "io.opentelemetry" } ]

Or, add this to slow down future updates of this dependency:

dependencyOverrides = [{
  pullRequests = { frequency = "@monthly" },
  dependency = { groupId = "io.opentelemetry" }
}]

labels: library-update, early-semver-minor, semver-spec-minor, commit-count:1