nixos/test-driver: Allow xwininfo to fail intermittently

[OPNA2608]

Untestable for me, as my hardware doesn't run into this issue. Will pull into #398413 and check if it fixes flakiness there.

wait_for_window can fail due to xwininfo running into an X error:

error: builder for '/nix/store/lf1nfgxj05919z944gvz39rn68ls3n7y-vm-test-run-lomiri-calculator-app-standalone.drv' failed with exit code 1;
       last 25 log lines:
       > subtest: lomiri calculator launches
       > machine: waiting for a window to appear
       > machine: must succeed: xwininfo -root -tree | sed 's/.*0x[0-9a-f]* \"\([^\"]*\)\".*/\1/; t; d'
       > (finished: must succeed: xwininfo -root -tree | sed 's/.*0x[0-9a-f]* \"\([^\"]*\)\".*/\1/; t; d', in 4.64 seconds)
       > machine: must succeed: xwininfo -root -tree | sed 's/.*0x[0-9a-f]* \"\([^\"]*\)\".*/\1/; t; d'
       > machine # X Error: 9: Bad Drawable
       > machine #   Request Major code: 14
       > machine #   ResourceID in failed request: 0x60005b
       > machine #   Serial number of failed request: 38
       > machine # X Error: 3: Bad Window
       > machine #   Request Major code: 15
       > machine #   ResourceID in failed request: 0x60005b
       > machine #   Serial number of failed request: 40
       > machine # xwininfo: error: Can't query window tree.
       > machine: output: IceDock
       > IceBottom
       > IceTopWin
       > IceWM 3.7.3 (Linux/aarch64)
       >
       > Test "lomiri calculator launches" failed with error: "command `xwininfo -root -tree | sed 's/.*0x[0-9a-f]* \"\([^\"]*\)\".*/\1/; t; d'` failed (exit code 1)"
       > cleanup
       > kill machine (pid 11)
       > qemu-system-aarch64: terminating on signal 15 from pid 8 (/nix/store/ic0fd07z8wg57idmw7q7iy7dc7md6x72-python3-3.12.9/bin/python3.12)
       > kill vlan (pid 9)
       > (finished: cleanup, in 0.01 seconds)
       For full logs, run 'nix log /nix/store/lf1nfgxj05919z944gvz39rn68ls3n7y-vm-test-run-lomiri-calculator-app-standalone.drv'.

Under the assumption that this is a temporary failure, rewrite get_window_names to not require the xwininfo | sed command to succeed at all times.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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