[io][HDF5File] remove `r+` mode from the valid mode

3 jobs for hdf5_scan_file_lock in 2 minutes and 33 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test Library
passed #131409
test:python3.5-stretch-pyqt5

00:01:13

passed #131410
test:python3.7_stretch_pyqt5

00:01:06

 
  Test Notbooks
passed #131411
test:test-tomoscan-tutorials

00:01:20