test: fix failing prompt test (#12847)

packages/opencode/test/session/prompt-variant.test.ts

@@ -6,6 +6,10 @@ import { tmpdir } from "../fixture/fixture"
 
 describe("session.prompt agent variant", () => {
   test("applies agent variant only when using agent model", async () => {
+    const prev = process.env.OPENAI_API_KEY
+    process.env.OPENAI_API_KEY = "test-openai-key"
+
+    try {
       await using tmp = await tmpdir({
         git: true,
         config: {
@@ -56,5 +60,9 @@ describe("session.prompt agent variant", () => {
           await Session.remove(session.id)
         },
       })
+    } finally {
+      if (prev === undefined) delete process.env.OPENAI_API_KEY
+      else process.env.OPENAI_API_KEY = prev
+    }
   })
 })