Ignore Pallas TPU tests when testing with the oldest supported libtpu

I missed adding this in from https://github.com/jax-ml/jax/blob/main/.github/workflows/cloud-tpu-ci-nightly.yml when I added the TPU jobs to the new CI workflows

PiperOrigin-RevId: 736094492

.github/workflows/pytest_tpu.yml

@@ -135,6 +135,8 @@ jobs:
             echo "Using oldest supported libtpu"
             $JAXCI_PYTHON -m uv pip install --pre libtpu-nightly==0.1.dev${{ env.LIBTPU_OLDEST_VERSION_DATE }} \
               -f https://storage.googleapis.com/jax-releases/libtpu_releases.html
+
+            echo "libtpu_version_type=oldest_supported_libtpu" >> $GITHUB_ENV
           else
             echo "Unknown libtpu version type: ${{ inputs.libtpu-version-type }}"
             exit 1

ci/run_pytest_tpu.sh

@@ -53,10 +53,19 @@ export JAX_SKIP_SLOW_TESTS=true
 echo "Running TPU tests..."
 
 if [[ "$JAXCI_RUN_FULL_TPU_TEST_SUITE" == "1" ]]; then
+  # We're deselecting all Pallas TPU tests in the oldest libtpu build. Mosaic
+  # TPU does not guarantee anything about forward compatibility (unless
+  # jax.export is used) and the 12 week compatibility window accumulates way
+  # too many failures.
+  IGNORE_FLAGS=""
+  if [ "${libtpu_version_type:-""}" == "oldest_supported_libtpu" ]; then
+    IGNORE_FLAGS="--ignore=tests/pallas"
+  fi
+
   # Run single-accelerator tests in parallel
   JAX_ENABLE_TPU_XDIST=true "$JAXCI_PYTHON" -m pytest -n="$JAXCI_TPU_CORES" --tb=short \
     --deselect=tests/pallas/tpu_pallas_test.py::PallasCallPrintTest \
-    --maxfail=20 -m "not multiaccelerator" tests examples
+    --maxfail=20 -m "not multiaccelerator" $IGNORE_FLAGS tests examples
 
   # Run Pallas printing tests, which need to run with I/O capturing disabled.
   TPU_STDERR_LOG_LEVEL=0 "$JAXCI_PYTHON" -m pytest -s \