.github/workflows/os_comp.yml: set HOME to /root on OpenSUSE

[the-horo]

D tests in CI are currently skipped on OpenSUSE:

2024-09-13T05:41:49.5905706Z ##[group]Run bash -c 'source /ci/env_vars.sh; cd $GITHUB_WORKSPACE; ./tools/run_with_cov.py ./run_tests.py $CI_ARGS'
2024-09-13T05:41:49.5906827Z bash -c 'source /ci/env_vars.sh; cd $GITHUB_WORKSPACE; ./tools/run_with_cov.py ./run_tests.py $CI_ARGS'
2024-09-13T05:41:49.5910232Z shell: sh -e {0}
2024-09-13T05:41:49.5910719Z env:
2024-09-13T05:41:49.5911076Z   ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true
2024-09-13T05:41:49.5911543Z   MESON_CI_JOBNAME: linux-opensuse-gcc
2024-09-13T05:41:49.5912026Z ##[endgroup]
2024-09-13T05:41:49.6638977Z /ci/env_vars.sh: line 12: /github/home/dlang/dmd-2.109.1/activate: No such file or directory
2024-09-13T05:41:50.2631396Z Meson build system 1.5.99 Project and Unit Tests
#### <snip>
2024-09-13T05:51:49.9153096Z  [SKIPPED]   failing: 80 dub library
2024-09-13T05:51:49.9154187Z Reason: test requires D compiler
2024-09-13T05:51:49.9160901Z  [SKIPPED]   failing: 81 dub executable
2024-09-13T05:51:49.9162680Z Reason: test requires D compiler
2024-09-13T05:51:49.9173974Z  [SKIPPED]   failing: 82 dub compiler    (warning_level=1)
2024-09-13T05:51:49.9175726Z Reason: not run because preconditions were not met
#### <snip>
2024-09-13T05:53:50.7814038Z 
2024-09-13T05:53:50.7814564Z Not running d tests.
2024-09-13T05:53:50.7814992Z 

[thesamesam]

Please include some information in the commit message too.