Cycles: Disable HIP-RT by default and mark as unstable

In blender-v4.5 some problematic commits were reverted, but for 5.0 we will
keep the changes and wait for the HIP SDK to be upgraded and hopefully fix
these issues.

Ref blender/blender#139836

intern/cycles/blender/addon/properties.py

@@ -1610,9 +1610,10 @@ class CyclesPreferences(bpy.types.AddonPreferences):
     )
 
     use_hiprt: BoolProperty(
-        name="HIP RT",
-        description="HIP RT enables AMD hardware ray tracing on RDNA2 and above",
-        default=True,
+        name="HIP RT (Unstable)",
+        description="HIP RT enables AMD hardware ray tracing on RDNA2 and above. This currently has known stability "
+        "issues, that are expected to be solved before the next release.",
+        default=False,
     )
 
     use_oneapirt: BoolProperty(