Add `pytest_markeval_namespace` hook.

Add a new hook , `pytest_markeval_namespace` which should return a dictionary.
This dictionary will be used to augment the "global" variables available to evaluate skipif/xfail/xpass markers.

Pseudo example

``conftest.py``:

.. code-block:: python
   def pytest_markeval_namespace():
       return {"color": "red"}
``test_func.py``:

.. code-block:: python
   @pytest.mark.skipif("color == 'blue'", reason="Color is not red")
   def test_func():
       assert False

2 files changed, 32 insertions, 0 deletions

diff --git a/src/_pytest/hookspec.py b/src/_pytest/hookspec.py
index 33ca782cf..e499b742c 100644
--- a/src/_pytest/hookspec.py
+++ b/src/_pytest/hookspec.py
@@ -809,6 +809,27 @@ def pytest_warning_recorded(
 
 
 # -------------------------------------------------------------------------
+# Hooks for influencing skipping
+# -------------------------------------------------------------------------
+
+
+def pytest_markeval_namespace(config: "Config") -> Dict[str, Any]:
+    """Called when constructing the globals dictionary used for
+    evaluating string conditions in xfail/skipif markers.
+
+    This is useful when the condition for a marker requires
+    objects that are expensive or impossible to obtain during
+    collection time, which is required by normal boolean
+    conditions.
+
+    .. versionadded:: 6.2
+
+    :param _pytest.config.Config config: The pytest config object.
+    :returns: A dictionary of additional globals to add.
+    """
+
+
+# -------------------------------------------------------------------------
 # error handling and internal debugging hooks
 # -------------------------------------------------------------------------
 
diff --git a/src/_pytest/skipping.py b/src/_pytest/skipping.py
index afc3610eb..9aacfecee 100644
--- a/src/_pytest/skipping.py
+++ b/src/_pytest/skipping.py
@@ -3,6 +3,7 @@ import os
 import platform
 import sys
 import traceback
+from collections.abc import Mapping
 from typing import Generator
 from typing import Optional
 from typing import Tuple
@@ -98,6 +99,16 @@ def evaluate_condition(item: Item, mark: Mark, condition: object) -> Tuple[bool,
             "platform": platform,
             "config": item.config,
         }
+        for dictionary in reversed(
+            item.ihook.pytest_markeval_namespace(config=item.config)
+        ):
+            if not isinstance(dictionary, Mapping):
+                raise ValueError(
+                    "pytest_markeval_namespace() needs to return a dict, got {!r}".format(
+                        dictionary
+                    )
+                )
+            globals_.update(dictionary)
         if hasattr(item, "obj"):
             globals_.update(item.obj.__globals__)  # type: ignore[attr-defined]
         try: