chore: Use VSCode engine 1.68 (May 2022)

[tomkerkhove]

Use VSCode engine 1.68 (May 2022) to be more up-to-date, similar to partner teams (who are often more aggressive):

• https://github.com/microsoft/powerplatform-vscode/blob/main/package.json#L54
• https://github.com/microsoft/vscode-azurecontainerapps/blob/main/package.json#L10
• https://github.com/microsoft/vscode-azurelogicapps/blob/main/package.json#L10
• https://github.com/microsoft/vscode-azureresourcegroups/blob/main/package.json#L10
• https://github.com/microsoft/vscode-azurefunctions/blob/main/package.json#L10
• https://github.com/microsoft/vscode-docker/blob/main/package.json#L2888