Help ROOT I/O of class in streamer field test

[vepadulano]

Attempt at fixing failures such as seen on MacOS beta:

  Error in <CloseStreamerInfoROOTFile>: Unique pointer unique_ptr<PolyBase,default_delete<PolyBase> > has zero data members.

See e.g. https://github.com/root-project/root/actions/runs/19197912794/job/54881579525?pr=20353#step:6:5580

[github-actions]

Test Results

    22 files      22 suites   3d 14h 9m 24s ⏱️
 3 738 tests  3 738 ✅ 0 💤 0 ❌
80 303 runs  80 303 ✅ 0 💤 0 ❌

Results for commit f9768ef.

[pcanal]

Let put this band-aid on for now, so the other PR are not distracted, but we need to resolved/understand this.

[hahnjo]

Unfortunately this didn't work, the build in master still fails with the same error: https://github.com/root-project/root/actions/runs/19250798263/job/55035175377 The reason is that this PR landed on macphsft34 which has

sftnight@macphsft34 ~ % sw_vers 
ProductName:		macOS
ProductVersion:		26.1
BuildVersion:		25B77
sftnight@macphsft34 ~ % clang --version
Apple clang version 17.0.0 (clang-1700.4.4.1)
Target: arm64-apple-darwin25.1.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

compared to

sftnight@macphsft35 ~ % sw_vers 
ProductName:		macOS
ProductVersion:		26.2
BuildVersion:		25C5031i
sftnight@macphsft35 ~ % clang --version
Apple clang version 17.0.0 (clang-1700.6.3.2)
Target: arm64-apple-darwin25.2.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

(btw the "correct" tag for commit messages is [ntuple])

[vepadulano]

I was mislead as well because today's nightly actually run well https://github.com/root-project/root/actions/runs/19251983040/job/55038655542

This can be reverted then