Remove the unsupported target framework

[Varorbc]

https://github.com/protocolbuffers/protobuf/blob/a30b25578a0435c9c692f9a54b7b060a234dc6b3/csharp/src/Google.Protobuf/Google.Protobuf.csproj#L11

The minimum version supported by the.net framework is 4.6.2 https://dotnet.microsoft.com/download/dotnet-framework

The minimum version supported by the.net is 6.0 https://dotnet.microsoft.com/zh-cn/download/dotnet

The recommended version for.net standard is 2.0 https://github.com/dotnet/designs/blob/main/accepted/2024/net-standard-recommendation.md

[github-actions[bot]]

We triage inactive PRs and issues in order to make it easier to find active work. If this issue should remain active or becomes active again, please add a comment.

This issue is labeled inactive because the last activity was over 90 days ago. This issue will be closed and archived after 14 additional days without activity.

[Varorbc]

ping

[github-actions[bot]]

We triage inactive PRs and issues in order to make it easier to find active work. If this issue should remain active or becomes active again, please add a comment.

This issue is labeled inactive because the last activity was over 90 days ago. This issue will be closed and archived after 14 additional days without activity.

[github-actions[bot]]

We triage inactive PRs and issues in order to make it easier to find active work. If this issue should remain active or becomes active again, please reopen it.

This issue was closed and archived because there has been no new activity in the 14 days since the inactive label was added.