TST: Skip test_rolling_var_numerical_issues on riscv64 platforms

The test is failing on riscv64.  The failure is reproducible under
qemu and on real hardware (VisionFive 2).

Updates pandas-dev#38921

Author: markdryan

pandas/compat/__init__.py

@@ -122,6 +122,18 @@ def is_platform_power() -> bool:
     return platform.machine() in ("ppc64", "ppc64le")
 
 
+def is_platform_riscv64() -> bool:
+    """
+    Checking if the running platform use riscv64 architecture.
+
+    Returns
+    -------
+    bool
+        True if the running platform uses riscv64 architecture.
+    """
+    return platform.machine() == "riscv64"
+
+
 def is_ci_environment() -> bool:
     """
     Checking if running in a continuous integration environment by checking

pandas/tests/window/test_rolling.py

@@ -10,6 +10,7 @@
     IS64,
     is_platform_arm,
     is_platform_power,
+    is_platform_riscv64,
 )
 
 from pandas import (
@@ -1081,7 +1082,7 @@ def test_rolling_sem(frame_or_series):
 
 
 @pytest.mark.xfail(
-    is_platform_arm() or is_platform_power(),
+    is_platform_arm() or is_platform_power() or is_platform_riscv64(),
     reason="GH 38921",
 )
 @pytest.mark.parametrize(