I'm seeing what appears to my uneducated eyes to be the same failure on Mojave, on a brand new machine which is entirely standalone:

12:16:00 0:00:07 load avg: 4.24 [133/416/1] test_posix failed
12:16:00 test test_posix failed -- Traceback (most recent call last):
12:16:00   File "/Users/jenkins/workspace/python-macos-build/Python-3.7.2/Lib/test/test_posix.py", line 1026, in test_getgrouplist
12:16:00     self.assertIn(group, posix.getgrouplist(user, group))
12:16:00 OSError: [Errno 25] Inappropriate ioctl for device
12:16:00 0:00:07 load avg: 4.24 [134/416/1] test_ast passed

System info:

pgabf-macos2:Python-3.7.2 jenkins$ gcc --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/usr/include/c++/4.2.1
Apple LLVM version 10.0.1 (clang-1001.0.46.3)
Target: x86_64-apple-darwin18.2.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

pgabf-macos2:Python-3.7.2 jenkins$ system_profiler SPSoftwareDataType
Software:

    System Software Overview:

      System Version: macOS 10.14.3 (18D42)
      Kernel Version: Darwin 18.2.0
      Boot Volume: Macintosh HD
      Boot Mode: Normal
      Computer Name: pgabf-macos2
      User Name: Jenkins (jenkins)
      Secure Virtual Memory: Enabled
      System Integrity Protection: Enabled
      Time since boot: 10 days 1:30

Happy to provide any additional info or try out patches if anyone wants.