doc: fix EncodingWarnings in examples (#11158)

Otherwise the warnings show in the regen output.

doc/en/example/nonpython/conftest.py

@@ -12,7 +12,7 @@ class YamlFile(pytest.File):
         # We need a yaml parser, e.g. PyYAML.
         import yaml
 
-        raw = yaml.safe_load(self.path.open())
+        raw = yaml.safe_load(self.path.open(encoding="utf-8"))
         for name, spec in sorted(raw.items()):
             yield YamlItem.from_parent(self, name=name, spec=spec)
 

doc/en/example/simple.rst

@@ -817,7 +817,7 @@ case we just write some information out to a ``failures`` file:
         # we only look at actual failing test calls, not setup/teardown
         if rep.when == "call" and rep.failed:
             mode = "a" if os.path.exists("failures") else "w"
-            with open("failures", mode) as f:
+            with open("failures", mode, encoding="utf-8") as f:
                 # let's also access a fixture for the fun of it
                 if "tmp_path" in item.fixturenames:
                     extra = " ({})".format(item.funcargs["tmp_path"])

doc/en/how-to/fixtures.rst

@@ -1698,7 +1698,7 @@ and declare its use in a test module via a ``usefixtures`` marker:
     class TestDirectoryInit:
         def test_cwd_starts_empty(self):
             assert os.listdir(os.getcwd()) == []
-            with open("myfile", "w") as f:
+            with open("myfile", "w", encoding="utf-8") as f:
                 f.write("hello")
 
         def test_cwd_again_starts_empty(self):

doc/en/how-to/tmp_path.rst

@@ -24,8 +24,8 @@ created in the `base temporary directory`_.
         d = tmp_path / "sub"
         d.mkdir()
         p = d / "hello.txt"
-        p.write_text(CONTENT)
+        p.write_text(CONTENT, encoding="utf-8")
-        assert p.read_text() == CONTENT
+        assert p.read_text(encoding="utf-8") == CONTENT
         assert len(list(tmp_path.iterdir())) == 1
         assert 0
 

doc/en/how-to/unittest.rst

@@ -207,10 +207,10 @@ creation of a per-test temporary directory:
         @pytest.fixture(autouse=True)
         def initdir(self, tmp_path, monkeypatch):
             monkeypatch.chdir(tmp_path)  # change to pytest-provided temporary directory
-            tmp_path.joinpath("samplefile.ini").write_text("# testdata")
+            tmp_path.joinpath("samplefile.ini").write_text("# testdata", encoding="utf-8")
 
         def test_method(self):
-            with open("samplefile.ini") as f:
+            with open("samplefile.ini", encoding="utf-8") as f:
                 s = f.read()
             assert "testdata" in s