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/validate.expressions.test.ts

@@ -1596,6 +1596,48 @@ jobs:
         expect(result).toEqual([]);
       });
 
+      it("allows runner.environment context", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - if: runner.environment == 'github-hosted'
+        run: echo hello`;
+
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([]);
+      });
+
+      it("allows runner.debug context", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - if: runner.debug == '1'
+        run: echo hello`;
+
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([]);
+      });
+
+      it("allows runner.workspace context", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - if: runner.workspace != ''
+        run: echo hello`;
+
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([]);
+      });
+
       it("allows env context", async () => {
         const input = `
 on: push