ci: explicitly change oom-{score}-adj before running tests

For some reason a user in GH actions is able to _decrease_ its oom score
even after dropping all capabilities (including CAP_SYS_RESOURCE), until
the oom score is changed explicitly after sudo:

$ systemd-detect-virt
microsoft
$ sudo su -
~# capsh --drop=all -- -c 'capsh --print; grep -H . /proc/self/oom*; choom -p $$ -n -101'
Current: =
Bounding set =
Ambient set =
Current IAB: !cap_chown,!cap_dac_override,!cap_dac_read_search,...,!cap_sys_resource,...,!cap_checkpoint_restore
Securebits: 00/0x0/1'b0
 secure-noroot: no (unlocked)
 secure-no-suid-fixup: no (unlocked)
 secure-keep-caps: no (unlocked)
 secure-no-ambient-raise: no (unlocked)
uid=0(root) euid=0(root)
gid=0(root)
groups=0(root)
Guessed mode: UNCERTAIN (0)
/proc/self/oom_adj:8
/proc/self/oom_score:1000
/proc/self/oom_score_adj:500
pid 22180's OOM score adjust value changed from 500 to -101
~# choom -p $$ -n 500
pid 22027's OOM score adjust value changed from 500 to 500
~# capsh --drop=all -- -c 'capsh --print; grep -H . /proc/self/oom*; choom -p $$ -n -101'
Current: =
Bounding set =
Ambient set =
...
uid=0(root) euid=0(root)
gid=0(root)
groups=0(root)
Guessed mode: UNCERTAIN (0)
/proc/self/oom_adj:8
/proc/self/oom_score:1000
/proc/self/oom_score_adj:500
choom: failed to set score adjust value: Permission denied

I have no idea what's going on, but it breaks
exec-oomscoreadjust-negative.service from test-execute when running
unprivileged.

.github/workflows/unit_tests.sh

@@ -58,6 +58,11 @@ for phase in "${PHASES[@]}"; do
             # part of test-execute gets skipped, since it can't run systemd-executor
             chmod o+x /home/runner
             capsh --drop=all -- -c "stat $PWD/meson.build"
+            # (Re)set the current oom-{score-}adj. For some reason a user on GH actions is able to _decrease_
+            # its oom-score even after dropping all capabilities (including CAP_SYS_RESOURCE), until the
+            # score is explicitly changed after sudo. No idea what's going on, but it breaks
+            # exec-oomscoreadjust-negative.service from test-execute when running unprivileged.
+            choom -p $$ -n 0
             ;;
         RUN|RUN_GCC|RUN_CLANG|RUN_CLANG_RELEASE)
             if [[ "$phase" =~ ^RUN_CLANG ]]; then