goffice: disable tests on powerpc64le

[ghost]

Description of changes

The goffice tests fail on powerpc64le due to its non-IEEE long double type having unexpected rounding behavior:

FAIL: test-format
===========================================
   goffice 0.10.51: tests/test-suite.log
===========================================

# TOTAL: 3
# PASS:  2
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0

.. contents:: :depth: 2

FAIL: test-format
=================

go_render_general: 1.9999999990000001 12 -> "1.999999999"
go_render_general: 1.9999999990000001 11 -> "1.999999999"
go_render_general: 1.9999999990000001 10 -> "1.99999999"
Expected "2"
**
ERROR:test-format.c:22:test_general_format_1: assertion failed: (0)
Bail out! ERROR:test-format.c:22:test_general_format_1: assertion failed: (0)
FAIL test-format (exit status: 134)

============================================================================
Testsuite summary for goffice 0.10.51
============================================================================
# TOTAL: 3
# PASS:  2
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0
============================================================================
See tests/test-suite.log
Please report to https://gitlab.gnome.org/GNOME/goffice/issues
============================================================================

Things done

• Built on platform(s)
  • powerpc64le-linux
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• Fits CONTRIBUTING.md.

[ghost]

See also #170402