fixes #22218; avoids cursor when copy is disabled (#23209)

fixes #22218

tests/arc/t22218.nim

@@ -0,0 +1,25 @@
+discard """
+  cmd: "nim c --mm:arc $file"
+  errormsg: "'=copy' is not available for type <Obj>; requires a copy because it's not the last read of 'chan[]'; routine: test"
+"""
+
+# bug #22218
+type Obj[T] = object
+  v: T
+
+proc `=copy`[T](
+    dest: var Obj[T],
+    source: Obj[T]
+  ) {.error: "A channel cannot be copied".}
+
+from system/ansi_c import c_calloc
+
+proc test() =
+    var v: bool = true
+    var chan = cast[ptr Obj[int]](c_calloc(1, csize_t sizeof(Obj[int])))
+    var copy = chan[]
+
+    echo chan.v
+    echo v
+
+test()