[io] read versioned class from file even if in-memory-class is unversioned

[ferdymercury]

This Pull request:

Changes or fixes:

Fixes https://its.cern.ch/jira/browse/ROOT-5306

Reproducer:

root
.L /tmp/MySubClass.cxx+
TFile f("/tmp/mysub.root", "RECREATE");
MySubClass msc;
msc.id = 33;
f.WriteObjectAny(&msc, "MySubClass", "msc");
f.Close();
.q
root
.L /tmp/MySubClassUnv.cxx+
auto file = TFile::Open("/tmp/mysub.root", "READ");
auto msc = file->Get<MySubClass>("msc")
(msc->id == 33)
.q

with MySubClass.cxx

class MySubClass { public: int id; ClassDef(MySubClass, 3) };

and MySubClassUnv.cxx

class MySubClass { public: int id; };

Checklist:

• tested changes locally
• updated the docs (if necessary)

[github-actions]

Test Results

    22 files      22 suites   3d 7h 3m 26s ⏱️
 3 828 tests  3 824 ✅ 1 💤 3 ❌
76 613 runs  76 601 ✅ 9 💤 3 ❌

For more details on these failures, see this check.

Results for commit 336f18d.

♻️ This comment has been updated with latest results.

[ferdymercury]

@pcanal
gentle reminder to 'squash on merge' (if you approve).

[dpiparo]

Thanks for these changes. They look good to me.
@pcanal do you think we can merge?

[pcanal]

Thanks!

[pcanal]

Closing and Reopening to rebase the PR and retest.

[dpiparo]

@pcanal this is to be considered all green: the 3 tests failing on alma9 march native are due to a glitch in the website infra.