GH-46684: [C++] Fix Meson configuration issue on Windows (#46685)

### Rationale for this change

This fixes an issue with the Meson configuration on Windows

### What changes are included in this PR?

Fix up incorrect variable name usage

### Are these changes tested?

Yes

### Are there any user-facing changes?

No

* GitHub Issue: #46684

Authored-by: Will Ayd <[email protected]>
Signed-off-by: Sutou Kouhei <[email protected]>

Author: WillAyd

cpp/src/arrow/util/meson.build

@@ -246,9 +246,9 @@ if host_machine.system() == 'windows'
     # This manifest enables long file paths on Windows 10+
     # See https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#enable-long-paths-in-windows-10-version-1607-and-later
     if cpp_compiler.get_id() == 'msvc'
-        utility_test_sources += ['io_util_test.manifest']
+        utility_test_srcs += ['io_util_test.manifest']
     else
-        utility_test_sources += ['io_util_test.rc']
+        utility_test_srcs += ['io_util_test.rc']
     endif
 endif