user: TestGetAdditionalGroups/group_entry_with_out-of-range_gid fails on 32-bit architectures (GOARCH=386 / arm)

Description

When running tests in github.com/moby/sys/user on 32-bit architectures (e.g. GOARCH=386 or GOARCH=arm), TestGetAdditionalGroups/group_entry_with_out-of-range_gid fails:

=== RUN   TestGetAdditionalGroups
=== RUN   TestGetAdditionalGroups/group_entry_with_out-of-range_gid
    user_test.go:651: Parse(struct { doc string; groups []string; expected []int; hasError bool }{doc:"group entry with out-of-range gid", groups:[]string{"toolarge"}, expected:[]int(nil), hasError:true}) expects error but has none
--- FAIL: TestGetAdditionalGroups (0.01s)
    --- FAIL: TestGetAdditionalGroups/group_entry_with_out-of-range_gid (0.00s)
FAIL	github.com/moby/sys/user	0.008s

Steps to Reproduce

cd user
GOARCH=386 go test -v . -run "TestGetAdditionalGroups/group_entry_with_out-of-range_gid"

Root Cause Analysis

1. In user/user_test.go, the test defines groupContent with:

   toolarge:x:2147483648:
   

   where 2147483648 is math.MaxInt32 + 1.

2. In user/user.go, parseParts() parses GID entries into *int via:

   case *int:
       *e, _ = strconv.Atoi(string(p))
   

   Conversion errors returned by strconv.Atoi are explicitly ignored (_).

3. On 64-bit systems (int is int64), strconv.Atoi("2147483648") succeeds and sets *e = 2147483648. GetAdditionalGroups() then checks if g.Gid < minID || g.Gid > maxID (where maxID is 2147483647), correctly returning ErrRange.

4. On 32-bit systems (int is int32), strconv.Atoi("2147483648") overflows int32 and returns strconv.ErrRange while setting *e = math.MaxInt32 (2147483647). Because the conversion error is discarded, g.Gid becomes 2147483647. Since 2147483647 <= maxID, GetAdditionalGroups() considers the GID valid, does not return an error, and the test fails.

Suggested Fix

parseParts (or Group.Gid / User.Uid / User.Gid parsing) should either:

1. Parse IDs as int64 (e.g. strconv.ParseInt(string(p), 10, 64)) or validate strconv.ErrRange before truncating/converting to int, or
2. Check whether the string value exceeds maxID (or check for strconv.ErrRange) when validating group/user entries so that 32-bit platforms reject out-of-range values consistently with 64-bit platforms.

Start with user/user_test.go around TestGetAdditionalGroups and user/user.go around parseParts, then run GOARCH=386 go test -v . -run "TestGetAdditionalGroups/group_entry_with_out-of-range_gid". Trace how the GID is parsed on 32-bit and 64-bit architectures. Done means the out-of-range group entry reliably returns the expected error on both architectures without regressing User or Group ID parsing.