Opening unseekable file sometimes succeeds

**Describe the bug**
A call to create/open an unseekable file (e.g. /dev/null) sometimes succeeds and returns a valid file ID.

**Expected behavior**
The H5Fcreate()/H5Fopen() call should fail by returning H5I_INVALID_HID.

**Platform (please complete the following information)**
Variable; see CI results [here](https://github.com/HDFGroup/hdf5/actions/runs/10562340838).

**Additional context**
This problem can be observed during `test_unseekable_file()` in `tfile.c`.