Fix build (#5086)

Run the mypy test suite using Ubuntu 18.04. Ubuntu 20.04 doesn't have a package for virtualenv on Python 2.

Also, curses.color_pair() now has a named argument.

.github/workflows/tests.yml

@@ -79,7 +79,8 @@ jobs:
 
   mypy-test-suite:
     name: Run the mypy test suite
-    runs-on: ubuntu-latest
+    # Ubuntu 20.04 doesn't have the Python 2 venv module.
+    runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2

stdlib/_curses.pyi

@@ -223,7 +223,14 @@ def beep() -> None: ...
 def can_change_color() -> bool: ...
 def cbreak(__flag: bool = ...) -> None: ...
 def color_content(__color_number: int) -> Tuple[int, int, int]: ...
-def color_pair(__color_number: int) -> int: ...
+
+# Changed in Python 3.8.8 and 3.9.2
+if sys.version_info >= (3, 8):
+    def color_pair(pair_number: int) -> int: ...
+
+else:
+    def color_pair(__color_number: int) -> int: ...
+
 def curs_set(__visibility: int) -> int: ...
 def def_prog_mode() -> None: ...
 def def_shell_mode() -> None: ...

tests/stubtest_whitelists/py38.txt

@@ -5,6 +5,8 @@ _collections_abc.AsyncGenerator.ag_running
 _collections_abc.ItemsView.__reversed__
 _collections_abc.KeysView.__reversed__
 _collections_abc.ValuesView.__reversed__
+# This was changed in Python 3.8.8.
+_curses.color_pair
 _thread.ExceptHookArgs
 _thread._ExceptHookArgs
 ast.Bytes.__new__
@@ -42,6 +44,8 @@ concurrent.futures.ProcessPoolExecutor.map
 contextvars.Context.__init__
 contextvars.Context.get
 copy.PyStringMap
+# This was changed in Python 3.8.8.
+curses.color_pair
 dataclasses.field
 email.message.MIMEPart.as_string
 enum.Enum._generate_next_value_

tests/stubtest_whitelists/py39.txt

@@ -13,6 +13,8 @@ _collections_abc.Generator.throw
 _collections_abc.ItemsView.__reversed__
 _collections_abc.KeysView.__reversed__
 _collections_abc.ValuesView.__reversed__
+# This was changed in Python 3.9.2.
+_curses.color_pair
 _dummy_thread
 ast.Bytes.__new__
 ast.Ellipsis.__new__
@@ -48,6 +50,8 @@ collections.abc.ValuesView.__reversed__
 contextvars.Context.__init__
 contextvars.Context.get
 copy.PyStringMap
+# This was changed in Python 3.9.2.
+curses.color_pair
 dataclasses.field
 dataclasses.InitVar.__class_getitem__  # stubtest bug. doesn't do the right thing with overload + implicit classmethod __class_getitem__
 dummy_threading