Fix typescript-eslint v8 compatibility in test configs

[Copilot]

TypeScript-ESLint v8 introduced breaking changes where project and projectService cannot be used together. When using ember-eslint-parser as a custom parser, the correct configuration differs between versions.

Changes

• Added version detection logic to flat-ts/eslint.config.mjs and gjs-types/.eslintrc.cjs
• For TypeScript-ESLint v8+: use only project: true (setting both project and projectService causes errors)
• For TypeScript-ESLint v6/v7: use both projectService: true and project: true
• Added unpublished-development-types/ directory to suppress benign tsconfig warnings

The fix ensures type-checked linting works correctly across all supported TypeScript-ESLint versions (v6, v7, and v8+) while avoiding the "Enabling 'project' does nothing when 'projectService' is enabled" error in v8.

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[NullVoxPopuli]

@copilot you have failures (and why'd you undo some of my fixes?)

[Copilot]

@copilot you have failures (and why'd you undo some of my fixes?)

Fixed in 15462c1. I had incorrectly removed the version detection logic. The issue is that TypeScript-ESLint v8+ errors when both project and projectService are set together, but when using ember-eslint-parser, we need project: true to provide type information. The correct solution:

• For v8+: use ONLY project (no projectService)
• For v6/v7: use both projectService and project

Restored the version detection from your original fix commit.