Behaviour of `get_os_name()` changed in EasyBuild v4.5.2

[ocaisa]

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Previously to #3930, EasyBuild would return a lower case name for the OS version, and this was expected by, for example, the GCC easyblock.

Unfortunately we now have the case where some easyblocks are expecting the lower case response (https://github.com/easybuilders/easybuild-easyblocks/blob/develop/easybuild/easyblocks/g/gcc.py#L195-L199 , https://github.com/easybuilders/easybuild-easyblocks/blob/develop/easybuild/easyblocks/t/tensorflow.py#L287-L288), and others take what they can get (https://github.com/easybuilders/easybuild-easyblocks/blob/develop/easybuild/easyblocks/a/abaqus.py#L88).

For GCC specifically, no-one has raised this issue so I guess the problem described in https://github.com/easybuilders/easybuild-easyblocks/issues/363 is actually no longer relevant? Having said that, we have seen cases in EESSI where having LIBRARY_PATH set for GCCcore would have beneficial results (see https://www.eessi.io/docs/using_eessi/building_on_eessi/#manually-building-software-on-top-of-eessi-without-easybuild for example).