Fix global decimal.MarshalJSONWithoutQuotes overwrite

[alecsammon]

The decimal.MarshalJSONWithoutQuotes is a global variable.

By setting this value then this can cause problems with any other code that does not expect this value to be changed.

Instead using a custom encoder to ensure that the marshalling behaviour is as expected without changing the global value ensure that this will not cause compatibility issues with other projects.

This code is covered both by existing tests, and an additional one in this PR.
(if the custom encode switch case is not added, but the global variables are, then the tests fail).

[alecsammon]

The test failure for Test Integration with Dolt and DoltgreSQL / test-integration (pull_request) I believe is unrelated to these changes - looks like the test may be pointing at a commit which has been rebased or deleted?

Or maybe just a timing issue - once main has finished building then maybe the reference will exist?

[nicktobey]

The test failure is odd. It's a new check that we added, and my best guess is that we have some GitHub action that runs whenever a team member creates a PR, but not when someone external creates a PR.

Let me verify that.

[nicktobey]

Alright, according to @Hydrocharged this is happening because the PR is coming from a fork: the CI action is trying to check out the change, but can't because it doesn't exist in our repo. For now, we can ignore this failure.

[nicktobey]

@alecsammon Thank you so much for the contribution!

[alecsammon]

Thank you!

[nicktobey]

Let us know if you have any other issues using go-mysql-server as a library and we'll get right on it! We have a 24-hour pledge when it comes to issues.