try to determine common prefix for paths in tarball after filtering out */init/* paths

[boegel]

Tested this with eessi-2023.06-software-linux-aarch64-a64fx-1719346462.tar.gz, with these changes I get the following as members_list (as expected):

['2023.06/init/easybuild/eb_hooks.py',
 '2023.06/software/linux/aarch64/a64fx/modules/all/BLIS/0.9.0-GCC-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/CMake/3.26.3-GCCcore-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/FFTW.MPI/3.3.10-gompi-2023a.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/FFTW/3.3.10-GCC-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/FlexiBLAS/3.3.1-GCC-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/OpenBLAS/0.3.23-GCC-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/Python/3.11.3-GCCcore-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/SQLite/3.42.0-GCCcore-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/ScaLAPACK/2.2.0-gompi-2023a-fb.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/Tcl/8.6.13-GCCcore-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/UnZip/6.0-GCCcore-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/cURL/8.0.1-GCCcore-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/foss/2023a.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/gompi/2023a.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/libarchive/3.6.2-GCCcore-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/libffi/3.4.4-GCCcore-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/modules/all/make/4.4.1-GCCcore-12.3.0.lua',
 '2023.06/software/linux/aarch64/a64fx/software/BLIS/0.9.0-GCC-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/CMake/3.26.3-GCCcore-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/FFTW.MPI/3.3.10-gompi-2023a',
 '2023.06/software/linux/aarch64/a64fx/software/FFTW/3.3.10-GCC-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/FlexiBLAS/3.3.1-GCC-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/OpenBLAS/0.3.23-GCC-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/Python/3.11.3-GCCcore-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/SQLite/3.42.0-GCCcore-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/ScaLAPACK/2.2.0-gompi-2023a-fb',
 '2023.06/software/linux/aarch64/a64fx/software/Tcl/8.6.13-GCCcore-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/UnZip/6.0-GCCcore-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/cURL/8.0.1-GCCcore-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/foss/2023a',
 '2023.06/software/linux/aarch64/a64fx/software/gompi/2023a',
 '2023.06/software/linux/aarch64/a64fx/software/libarchive/3.6.2-GCCcore-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/libffi/3.4.4-GCCcore-12.3.0',
 '2023.06/software/linux/aarch64/a64fx/software/make/4.4.1-GCCcore-12.3.0']

[bedroge]

Failing CI checks for ubuntu 22.04 are completely unrelated to the changes in this PR, so I'm going to ignore those.