Update to .NET 5 SDK

[stevejgordon]

One interesting side-effect is a change to System.Text.Json which meant that ErrorWithNullRootCausesTests in the Tests project broke. Deserialisation now attempts to use ctors with parameters. The parameterless ctor is internal, and despite being reachable System.Text.Json is still preferring the ctor with params. However, it expects these to match the property names in the JSON so throws an exception.

A downside of this is we open up the parameterless constructor. Open to other suggestions here. A wider concern may be how this deserialisation behaves today for anyone using the library in a 5.0 runtime.

[Mpdreamz]

LGTM, getting there! 👍

[github-actions]

The backport to 7.10 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-7.10 7.10
# Navigate to the new working tree
cd .worktrees/backport-7.10
# Create a new branch
git switch --create backport-5099-to-7.10
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick ---mainline 1 fa2edcc435dd9ede14e57dd75ed3c8d9d417d28b
# Push it to GitHub
git push --set-upstream origin backport-5099-to-7.10
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-7.10

Then, create a pull request where the base branch is 7.10 and the compare/head branch is backport-5099-to-7.10.

[github-actions]

The backport to 7.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-7.x 7.x
# Navigate to the new working tree
cd .worktrees/backport-7.x
# Create a new branch
git switch --create backport-5099-to-7.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick ---mainline 1 fa2edcc435dd9ede14e57dd75ed3c8d9d417d28b
# Push it to GitHub
git push --set-upstream origin backport-5099-to-7.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-7.x

Then, create a pull request where the base branch is 7.x and the compare/head branch is backport-5099-to-7.x.