fixes #10542; suppresses varargs conversion warnings (#22757)

fixes #10542
revives and close #20169

tests/errmsgs/t10542.nim

@@ -0,0 +1,24 @@
+discard """
+  matrix: "--hintaserror:ConvFromXtoItselfNotNeeded"
+"""
+
+# bug #10542
+
+proc f(args: varargs[string, string], length: int) =
+  doAssert args.len == length
+
+# main use case that requires type conversion (no warning here)
+f("a", "b", 2)
+f("a", 1)
+
+
+proc m(args: varargs[cstring, cstring]) =
+  doAssert args.len == 2
+
+# main use case that requires type conversion (no warning here)
+m("a", "b")
+
+# if an argument already is cstring there's a warning
+let x: cstring = "x"
+m("a", x)
+m(x, "a")