Fix CI test segfault: clamp stack ulimit before odin test

Root cause found via gdb backtrace on the runner (thread::pool_init
crashed from main -> testing runner): the CI container sets
`ulimit -s unlimited`, so getrlimit(RLIMIT_STACK) returns RLIM_INFINITY.
core:thread passes that to pthread_attr_setstacksize, pthread_create
fails, and thread.create() returns nil, which core:testing's pool_init
dereferences without a nil check. Reproduced and confirmed fixed in an
ubuntu:24.04 container with the same Odin build. `just test` now clamps
the stack limit before running odin test. Also removes the gdb
diagnostic step added to debug this.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitea/workflows/gitea-build.yaml

@@ -30,18 +30,6 @@ jobs:
       - name: Test
         run: just test
 
-      - name: Debug Segfault
-        if: failure()
-        run: |
-          uname -a
-          cat /etc/os-release || true
-          clang --version
-          ulimit -a
-          free -h || true
-          SUDO=""; command -v sudo >/dev/null && SUDO=sudo
-          $SUDO apt-get install -y --no-install-recommends gdb >/dev/null
-          gdb -batch -ex run -ex bt -ex "info registers" build/tests
-
       - name: Build
         run: just release