ci(itcm): bump px4-dev container and drop pip install

The image now ships pyelftools, so the job no longer has to fetch it from
PyPI on every run. That install was a recurring failure: 502s from
files.pythonhosted.org killed 6 ITCM jobs in the last 30 days.

Removing the step matters as much as the bump. Left in place it would still
reach PyPI for the symforce line, which the check has never needed:
Tools/itcm_check.py imports only elftools.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/workflows/itcm_check.yml

@@ -24,7 +24,7 @@ jobs:
     name: Checking ${{ matrix.target }}
     runs-on: [runs-on,runner=4cpu-linux-x64,image=ubuntu24-full-x64,"run-id=${{ github.run_id }}",spot=false,extras=s3-cache]
     container:
-      image: ghcr.io/px4/px4-dev:v1.17.0-rc2
+      image: ghcr.io/px4/px4-dev:v1.18.0-beta1-327-ga7aecfb9fb1
     strategy:
       fail-fast: false
       matrix:
@@ -65,9 +65,6 @@ jobs:
       - name: Copy built ELF
         run: cp ./build/**/*.elf ./built.elf
 
-      - name: Install itcm-check dependencies
-        run: pip3 install -r Tools/setup/optional-requirements.txt --break-system-packages
-
       - name: Execute the itcm-check
         run: python3 Tools/itcm_check.py --elf-file built.elf --script-files ${{ matrix.scripts }}