ci: Only use the Ubuntu TDX machine in the CI

We've been hitting issues with the CentOS 9 Stream machine, which Intel
doesn't have cycles to debug.

After raising this up in the Confidential Containers community meeting
we got the green light from Red Hat (Ariel Adam) to just disable the CI
based on CentOS 9 Stream for now.

Signed-off-by: Fabiano Fidêncio <fabiano@fidencio.org>

.github/actionlint.yaml

@@ -21,5 +21,4 @@ self-hosted-runner:
     - sev-snp
     - s390x
     - s390x-large
-    - tdx-no-attestation
-    - tdx-attestation
+    - tdx

.github/workflows/run-kata-coco-tests.yaml

@@ -36,15 +36,7 @@ jobs:
           - nydus
         pull-type:
           - guest-pull
-        k8s-test-host-type:
-          - baremetal-attestation
-          - baremetal-no-attestation
-        include:
-          - k8s-test-host-type: baremetal-attestation
-            machine: tdx-attestation
-          - k8s-test-host-type: baremetal-no-attestation
-            machine: tdx-no-attestation
-    runs-on: ${{ matrix.machine }}
+    runs-on: tdx
     env:
       DOCKER_REGISTRY: ${{ inputs.registry }}
       DOCKER_REPO: ${{ inputs.repo }}
@@ -54,7 +46,7 @@ jobs:
       KUBERNETES: "vanilla"
       USING_NFD: "true"
       KBS: "true"
-      K8S_TEST_HOST_TYPE: ${{ matrix.k8s-test-host-type }}
+      K8S_TEST_HOST_TYPE: "baremetal"
       KBS_INGRESS: "nodeport"
       SNAPSHOTTER: ${{ matrix.snapshotter }}
       PULL_TYPE: ${{ matrix.pull-type }}
@@ -83,17 +75,14 @@ jobs:
         run: bash tests/integration/kubernetes/gha-run.sh deploy-kata-tdx
 
       - name: Uninstall previous `kbs-client`
-        if: ${{ matrix.machine != 'tdx-no-attestation' }}
         timeout-minutes: 10
         run: bash tests/integration/kubernetes/gha-run.sh uninstall-kbs-client
 
       - name: Deploy CoCo KBS
-        if: ${{ matrix.machine != 'tdx-no-attestation' }}
         timeout-minutes: 10
         run: bash tests/integration/kubernetes/gha-run.sh deploy-coco-kbs
 
       - name: Install `kbs-client`
-        if: ${{ matrix.machine != 'tdx-no-attestation' }}
         timeout-minutes: 10
         run: bash tests/integration/kubernetes/gha-run.sh install-kbs-client
 
@@ -114,7 +103,7 @@ jobs:
         run: bash tests/integration/kubernetes/gha-run.sh cleanup-snapshotter
 
       - name: Delete CoCo KBS
-        if: ${{ always() && matrix.machine != 'tdx-no-attestation' }}
+        if: always()
         run: bash tests/integration/kubernetes/gha-run.sh delete-coco-kbs
 
       - name: Delete CSI driver