ci: disable parallel building for ps2

The ps2 builds were flaky.

https://github.com/ps2dev/ps2dev/issues/67

.github/workflows/ps2.yml

@@ -36,7 +36,7 @@ jobs:
           -DCMAKE_INSTALL_PREFIX=cmake_prefix \
           -DCMAKE_BUILD_TYPE=Release
     - name: Build (CMake)
-      run: cmake --build build --config Release --verbose --parallel
+      run: cmake --build build --config Release --verbose -- -j 1
     - name: Install (CMake)
       run: |
         set -eu
@@ -45,7 +45,7 @@ jobs:
         ( cd cmake_prefix; find ) | LC_ALL=C sort -u
     - name: Package (CPack)
       run: |
-        cmake --build build/ --config Release --target package
+        cmake --build build/ --config Release --target package -- -j 1
 
     - name: Verify CMake configuration files
       run: |
@@ -55,7 +55,7 @@ jobs:
           -DTEST_SHARED=FALSE \
           -DCMAKE_PREFIX_PATH=${{ env.SDL3_DIR }} \
           -DCMAKE_BUILD_TYPE=Release
-        cmake --build cmake_config_build --verbose
+        cmake --build cmake_config_build --verbose -- -j 1
     - name: Verify sdl3.pc
       run: |
         export CC=mips64r5900el-ps2-elf-gcc