Deprecation of msg= for both pytest.skip() and pytest.fail(). (#8950)

* porting pytest.skip() to use reason=, adding tests

* avoid adding **kwargs, it breaks other functionality, use optional msg= instead

* deprecation of `pytest.fail(msg=...)`

* fix bug with not capturing the returned reason value

* pass reason= in acceptance async tests instead of msg=

* finalising deprecations of `msg` in `pytest.skip()` and `pytest.fail()`

* Update doc/en/deprecations.rst

Co-authored-by: Bruno Oliveira <nicoddemus@gmail.com>

* Update doc/en/deprecations.rst

Co-authored-by: Bruno Oliveira <nicoddemus@gmail.com>

* fix failing test after upstream merge

* adding deprecation to `pytest.exit(msg=...)`

* add docs for pytest.exit deprecations

* finalising deprecation of msg for pytest.skip, pytest.exit and pytest.fail

* hold a reference to the Scope instance to please mypy

Co-authored-by: Bruno Oliveira <nicoddemus@gmail.com>

testing/deprecated_test.py

@@ -200,6 +200,64 @@ def test_warns_none_is_deprecated():
             pass
 
 
+class TestSkipMsgArgumentDeprecated:
+    def test_skip_with_msg_is_deprecated(self, pytester: Pytester) -> None:
+        p = pytester.makepyfile(
+            """
+            import pytest
+
+            def test_skipping_msg():
+                pytest.skip(msg="skippedmsg")
+            """
+        )
+        result = pytester.runpytest(p)
+        result.stdout.fnmatch_lines(
+            [
+                "*PytestDeprecationWarning: pytest.skip(msg=...) is now deprecated, "
+                "use pytest.skip(reason=...) instead",
+                '*pytest.skip(msg="skippedmsg")*',
+            ]
+        )
+        result.assert_outcomes(skipped=1, warnings=1)
+
+    def test_fail_with_msg_is_deprecated(self, pytester: Pytester) -> None:
+        p = pytester.makepyfile(
+            """
+            import pytest
+
+            def test_failing_msg():
+                pytest.fail(msg="failedmsg")
+            """
+        )
+        result = pytester.runpytest(p)
+        result.stdout.fnmatch_lines(
+            [
+                "*PytestDeprecationWarning: pytest.fail(msg=...) is now deprecated, "
+                "use pytest.fail(reason=...) instead",
+                '*pytest.fail(msg="failedmsg")',
+            ]
+        )
+        result.assert_outcomes(failed=1, warnings=1)
+
+    def test_exit_with_msg_is_deprecated(self, pytester: Pytester) -> None:
+        p = pytester.makepyfile(
+            """
+            import pytest
+
+            def test_exit_msg():
+                pytest.exit(msg="exitmsg")
+            """
+        )
+        result = pytester.runpytest(p)
+        result.stdout.fnmatch_lines(
+            [
+                "*PytestDeprecationWarning: pytest.exit(msg=...) is now deprecated, "
+                "use pytest.exit(reason=...) instead",
+            ]
+        )
+        result.assert_outcomes(warnings=1)
+
+
 def test_deprecation_of_cmdline_preparse(pytester: Pytester) -> None:
     pytester.makeconftest(
         """