fix(task): Align task group validation with VS Code (#13075)

* fix(task): Align task group validation with VSCode

In VS Code, the following is considered correct in a `tasks.json`:
```
"group": {"kind": "build","isDefault": false}
```

In Theia, however, this is considered an error. This also prevents such
tasks to be listed correctly when e.g. executing the command
"Run Build Task".

Contributed on behalf of STMicroelectronics.

Fixes #12917

CHANGELOG.md

@@ -9,6 +9,7 @@
 - [task] prevent task widget title from being changed by task process [#13003](https://github.com/eclipse-theia/theia/pull/13003)
 - [vscode] added Notebook CodeActionKind [#13093](https://github.com/eclipse-theia/theia/pull/13093) - contributed on behalf of STMicroelectronics
 - [vscode] added support to env.ondidChangeShell event [#13097](https://github.com/eclipse-theia/theia/pull/13097) - contributed on behalf of STMicroelectronics
+- [task] support `isDefault: false` in task group definition [#13075](https://github.com/eclipse-theia/theia/pull/13075) - contributed on behalf of STMicroelectronics
 
 ## v1.43.0 - 10/26/2023
 

packages/task/src/browser/task-schema-updater.ts

@@ -294,15 +294,27 @@ const commandAndArgs = {
 const group: IJSONSchema = {
     oneOf: [
         {
-            type: 'string'
+            type: 'string',
+            enum: ['build', 'test', 'none'],
+            enumDescriptions: [
+                'Marks the task as a build task accessible through the \'Run Build Task\' command.',
+                'Marks the task as a test task accessible through the \'Run Test Task\' command.',
+                'Assigns the task to no group'
+            ]
         },
         {
             type: 'object',
             properties: {
                 kind: {
                     type: 'string',
                     default: 'none',
-                    description: 'The task\'s execution group.'
+                    description: 'The task\'s execution group.',
+                    enum: ['build', 'test', 'none'],
+                    enumDescriptions: [
+                        'Marks the task as a build task accessible through the \'Run Build Task\' command.',
+                        'Marks the task as a test task accessible through the \'Run Test Task\' command.',
+                        'Assigns the task to no group'
+                    ]
                 },
                 isDefault: {
                     type: 'boolean',
@@ -312,20 +324,6 @@ const group: IJSONSchema = {
             }
         }
     ],
-    enum: [
-        { kind: 'build', isDefault: true },
-        { kind: 'test', isDefault: true },
-        'build',
-        'test',
-        'none'
-    ],
-    enumDescriptions: [
-        'Marks the task as the default build task.',
-        'Marks the task as the default test task.',
-        'Marks the task as a build task accessible through the \'Run Build Task\' command.',
-        'Marks the task as a test task accessible through the \'Run Test Task\' command.',
-        'Assigns the task to no group'
-    ],
     // eslint-disable-next-line max-len
     description: 'Defines to which execution group this task belongs to. It supports "build" to add it to the build group and "test" to add it to the test group.'
 };