chore(api-core): restore fail_under=100 in .coveragerc (#17768)

`fail_under` was previously adjusted down to `99` because coverage
reports included helper lines inside test files
(`tests/unit/test_operations_rest_client.py`). In non-`async_rest`
matrix sessions, conditional `if GOOGLE_AUTH_AIO_INSTALLED:` checks
inside test runner files were flagged as un-executed lines, artificially
dragging down total reported coverage.

- Configured `omit = tests/*, */tests/*` under `[report]` in
`.coveragerc` so coverage reporting evaluates threshold enforcement
(`fail_under`) strictly against the `google.api_core` source library
rather than test execution helper code.
- Restored `fail_under = 100` in `.coveragerc`.
Towards #17459 🦕

Author: ohmayr

packages/google-api-core/.coveragerc

@@ -2,8 +2,11 @@
 branch = True
 
 [report]
-fail_under = 99
+fail_under = 100
 show_missing = True
+omit =
+    tests/*
+    */tests/*
 exclude_lines =
     # Re-enable the standard pragma
     pragma: NO COVER

packages/google-api-core/google/api_core/gapic_v1/requests.py

@@ -21,8 +21,8 @@
 if they are not already set.
 """
 
-from typing import Union
 import uuid
+from typing import Union
 
 import google.protobuf.message
 

packages/google-api-core/tests/unit/gapic/test_requests.py

@@ -19,7 +19,6 @@
 
 from google.api_core.gapic_v1.requests import setup_request_id
 
-
 # --- Mock Request Helper Classes ---
 
 

packages/google-api-core/tests/unit/operations_v1/test_operations_client.py

@@ -100,3 +100,52 @@ def test_cancel_operation():
 
 def test_operations_client_config():
     assert operations_client_config.config["interfaces"]
+
+
+def test_operations_v1_transport_base_to_dict_protobuf_versions(monkeypatch):
+    from google.auth import credentials as ga_credentials
+    from google.longrunning import operations_pb2
+
+    from google.api_core.operations_v1.transports import base
+
+    message = operations_pb2.Operation(name="test_op")
+    transport = base.OperationsTransport(
+        credentials=ga_credentials.AnonymousCredentials()
+    )
+
+    calls = []
+
+    def mock_message_to_dict(*args, **kwargs):
+        calls.append(kwargs)
+        return {"name": "test_op"}
+
+    monkeypatch.setattr(base.json_format, "MessageToDict", mock_message_to_dict)
+
+    monkeypatch.setattr(base, "PROTOBUF_VERSION", "3.20.0")
+    res3 = transport._convert_protobuf_message_to_dict(message)
+    assert res3.get("name") == "test_op"
+    assert "including_default_value_fields" in calls[-1]
+
+    monkeypatch.setattr(base, "PROTOBUF_VERSION", "5.26.0")
+    res5 = transport._convert_protobuf_message_to_dict(message)
+    assert res5.get("name") == "test_op"
+    assert "always_print_fields_with_no_presence" in calls[-1]
+
+
+def test_operations_v1_init_import_error_fallback(monkeypatch):
+    import importlib
+
+    import google.api_core.operations_v1 as op_v1
+
+    orig_import = __import__
+
+    def mock_import(name, globals=None, locals=None, fromlist=(), level=0):
+        if "operations_rest_client_async" in name or (
+            fromlist and "AsyncOperationsRestClient" in fromlist
+        ):
+            raise ImportError("Simulated async rest import error")
+        return orig_import(name, globals, locals, fromlist, level)
+
+    monkeypatch.setattr("builtins.__import__", mock_import)
+    monkeypatch.setattr(op_v1, "_has_async_rest", True)
+    importlib.reload(op_v1)