Update dependency Serilog.Enrichers.Thread to v4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
Serilog.Enrichers.Thread (source)	3.1.0 -> 4.0.0

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Release Notes

serilog/serilog-enrichers-thread (Serilog.Enrichers.Thread)

### [`v4.0.0`](https://togithub.com/serilog/serilog-enrichers-thread/releases/tag/v4.0.0) - [#​13](https://togithub.com/serilog/serilog-enrichers-thread/issues/13) - code cleanup ([@​sungam3r](https://togithub.com/sungam3r)) - [#​14](https://togithub.com/serilog/serilog-enrichers-thread/issues/14) - README improvements ([@​StefanOssendorf](https://togithub.com/StefanOssendorf)) - [#​16](https://togithub.com/serilog/serilog-enrichers-thread/issues/16) - add caching to enrichers ([@​sungam3r](https://togithub.com/sungam3r)) - [#​18](https://togithub.com/serilog/serilog-enrichers-thread/issues/18) - build updates ([@​Numpsy](https://togithub.com/Numpsy)) - [#​20](https://togithub.com/serilog/serilog-enrichers-thread/issues/20) - bump Serilog dependency to support Unity ([@​bdovaz](https://togithub.com/bdovaz)) - [#​21](https://togithub.com/serilog/serilog-enrichers-thread/issues/21) - enable nullability annotations ([@​Numpsy](https://togithub.com/Numpsy)) - [#​22](https://togithub.com/serilog/serilog-enrichers-thread/issues/22) - update to Serilog 4, update explicit TFMs to match, internalize the enricher classes as described for the Environment enricher in [https://github.com/serilog/serilog-enrichers-environment/pull/63](https://togithub.com/serilog/serilog-enrichers-environment/pull/63) ([@​Numpsy](https://togithub.com/Numpsy))

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