fix(ip): fix CI failures in fuzz test and bash comparison tests

builtins/tests/ip/ip_fuzz_test.go

@@ -154,7 +154,7 @@ func FuzzIPSubcommand(f *testing.F) {
 		if code == -1 {
 			return // shell/parse error before the builtin ran — not our bug
 		}
-		if code != 0 && code != 1 {
+		if code != 0 && code != 1 && code != 255 {
 			t.Errorf("ip %q: unexpected exit code %d", subcmd, code)
 		}
 		if timedOut {

builtins/tests/ip/testdata/fuzz/FuzzIPSubcommand/ffdc891dc1bd740f

@@ -0,0 +1,2 @@
+go test fuzz v1
+string("route 0")

tests/scenarios/cmd/ip/errors/route_unknown_subcmd.yaml

@@ -1,5 +1,6 @@
 # ip route <unknown> exits 255 with iproute2-compatible "unknown" message.
 description: ip route with an unknown subcommand exits 255.
+skip_assert_against_bash: true # ip is a rshell builtin; bash does not have it
 input:
   script: |+
     ip route unknowncmd

tests/scenarios/cmd/ip/route_case_insensitive/get_uppercase.yaml

@@ -1,6 +1,7 @@
 # ip route GET (uppercase) is rejected — subcommand parsing is case-sensitive,
 # matching real iproute2 behavior.
 description: ip route uppercase subcommand (GET) is rejected (case-sensitive, matches iproute2).
+skip_assert_against_bash: true # ip is a rshell builtin; bash does not have it
 input:
   script: |+
     ip route GET