feat: Support System.Diagnostics.DiagnosticSource version 10.*

[bstordrup]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

Provide links to any issues in this repository or elsewhere relating to this pull request.

Closes #253

Describe the solution you've provided

Raised the upper version range limit on System.Diagnostics.DiagnosticSource to 11 instead of 10

Describe alternatives you've considered

Considered to completely remove the upper limit, but decided for the upper limit raise as done in an earlier pull request (#149) to support version 9x of the same library.

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Note

Low Risk
Low risk dependency-range change limited to the telemetry package project file; main risk is unexpected compatibility issues when consumers resolve newer DiagnosticSource versions.

Overview
Updates LaunchDarkly.ServerSdk.Telemetry.csproj to widen the System.Diagnostics.DiagnosticSource dependency upper bound from <10 to <11 for netstandard2.0/net462, enabling compatibility with 10.x versions (while keeping net8.0 relying on the built-in package).

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[bstordrup]

@launchdarkly/team-sdk-net, what is status?