Disable another setup test case

FAILED tests_old/test_setup.py::test_get_tag - AssertionError: assert
'macosx_10_9_x86_64' == 'macosx_10_9_universal2'

The actual result is correct, the test expectation wrong.
sourcebuild tagging was recently fixed not to produce universal2.

setupsrc/pypdfium2_setup/packaging_base.py

@@ -349,7 +349,7 @@ def get_wheel_tag(pl_name):
     elif pl_name == PlatNames.sourcebuild:
         # sysconfig.get_platform() may return universal2 on macOS. However, the binaries built here should be considered architecture-specific.
         # The reason why we don't simply do `if Host.platform: return get_wheel_tag(Host.platform) else ...` is that version info for pdfium-binaries does not have to match the sourcebuild host.
-        # NOTE On Linux, this just returns f"linux_{arch}" (which is a valid wheel tag). Leave it as-is since we don't know how to determine the build's lowest compatible libc. The caller may re-tag the wheel manually if desired.
+        # NOTE On Linux, this just returns f"linux_{arch}" (which is a valid wheel tag). Leave it as-is since we don't know the build's lowest compatible libc. The caller may re-tag using the wheel module's CLI.
         tag = sysconfig.get_platform().replace("-", "_").replace(".", "_")
         if tag.startswith("macosx") and tag.endswith("universal2"):
             tag = tag[:-len("universal2")] + Host._machine_name

tests_old/test_setup.py

@@ -58,7 +58,8 @@ def all_platnames():
     (PlatNames.windows_x64,    "win_amd64"),
     (PlatNames.windows_arm64,  "win_arm64"),
     (PlatNames.windows_x86,    "win32"),
-    (PlatNames.sourcebuild,    sysconfig.get_platform().replace('-','_').replace('.','_')),
+    # FIXME not sure how to test this
+    # (PlatNames.sourcebuild,    ...),
 )