Add missing runner context properties (environment, debug, workspace) (#241)

Fixes #78, #121

Adds three missing properties to the runner context:
- runner.environment: The runner environment (github-hosted or self-hosted)
- runner.debug: Set to '1' when step debug logging is enabled via ACTIONS_STEP_DEBUG
- runner.workspace: The runner-specific working directory path for the job

These are documented official properties that were causing false 'Context access might be invalid' warnings.

languageservice/src/complete.expressions.test.ts

@@ -299,7 +299,16 @@ jobs:
         "on: push\njobs:\n  build:\n    runs-on: ubuntu-latest\n    environment:\n      url: ${{ runner.| }}\n    steps:\n      - run: echo";
       const result = await complete(...getPositionFromCursor(input), {contextProviderConfig});
 
-      expect(result.map(x => x.label)).toEqual(["arch", "name", "os", "temp", "tool_cache"]);
+      expect(result.map(x => x.label)).toEqual([
+        "arch",
+        "debug",
+        "environment",
+        "name",
+        "os",
+        "temp",
+        "tool_cache",
+        "workspace"
+      ]);
     });
 
     describe("job if", () => {