Make host tests independent of global git identity

CI failed on the first real PR because five test commits relied on
a global user.name/user.email, which GitHub runners do not set.
Pass -c user.name=Test -c user.email=test@example.com on every
test commit, matching the helper that already does this for the
other tests. host.py worktree commits inherit the repo config
set by _init_git_repo, so they needed no change.

tests/test_host.py

@@ -93,7 +93,7 @@ class MergeVerifyTest(unittest.TestCase):
                 "        self.assertEqual(f(), 1)\n")
         (tests_dir / "test_mod.py").write_text(body, encoding="utf-8")
         subprocess.run(["git", "add", "-A"], cwd=tmp, check=True)
-        subprocess.run(["git", "commit", "-qm", "initial"], cwd=tmp,
+        subprocess.run(["git", "-c", "user.name=Test", "-c", "user.email=test@example.com", "commit", "-qm", "initial"], cwd=tmp,
                        check=True)
         # worktree 手动建：模拟 host 的 worktree/分支
         subprocess.run(["git", "worktree", "add", os.path.join(tmp, "wt"),
@@ -142,7 +142,7 @@ class MergeVerifyTest(unittest.TestCase):
             Path(tmp, "mod.py").write_text("def f():\n    return 1\n",
                                            encoding="utf-8")
             subprocess.run(["git", "add", "-A"], cwd=tmp, check=True)
-            subprocess.run(["git", "commit", "-qm", "initial"], cwd=tmp,
+            subprocess.run(["git", "-c", "user.name=Test", "-c", "user.email=test@example.com", "commit", "-qm", "initial"], cwd=tmp,
                            check=True)
             # 分支1：加 add2
             subprocess.run(["git", "worktree", "add",
@@ -458,7 +458,7 @@ class GithubPRTest(unittest.TestCase):
             _init_git_repo(tmp)
             Path(tmp, "f.txt").write_text("x\n")
             subprocess.run(["git", "add", "-A"], cwd=tmp, check=True)
-            subprocess.run(["git", "commit", "-qm", "initial"],
+            subprocess.run(["git", "-c", "user.name=Test", "-c", "user.email=test@example.com", "commit", "-qm", "initial"],
                            cwd=tmp, check=True)
             task = {"name": "t", "branch": "host/t", "status": "completed",
                     "prompt": "do it"}
@@ -473,12 +473,12 @@ class GithubPRTest(unittest.TestCase):
             _init_git_repo(repo)
             Path(repo, "f.txt").write_text("x\n")
             subprocess.run(["git", "add", "-A"], cwd=repo, check=True)
-            subprocess.run(["git", "commit", "-qm", "initial"],
+            subprocess.run(["git", "-c", "user.name=Test", "-c", "user.email=test@example.com", "commit", "-qm", "initial"],
                            cwd=repo, check=True)
             subprocess.run(["git", "checkout", "-qb", "host/t1"],
                            cwd=repo, check=True)
             Path(repo, "f.txt").write_text("y\n")
-            subprocess.run(["git", "commit", "-qam", "change"],
+            subprocess.run(["git", "-c", "user.name=Test", "-c", "user.email=test@example.com", "commit", "-qam", "change"],
                            cwd=repo, check=True)
             remote = os.path.join(tmp, "remote.git")
             subprocess.run(["git", "init", "--bare", "-q", remote],