ci(#5733): pin podman to 4.x to avoid crun incompatibility

.github/scripts/install-podman.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Pin and install podman, working around a crun incompatibility on some
+# runner images.
+#
+# Runner images occasionally pre-install podman 5.x paired with a crun too
+# old to support it, breaking sandbox creation with "crun: unknown version
+# specified". Pin to the 4.x series, which matches the crun shipped on these
+# images, until GitHub Actions runner images ship a compatible crun pairing.
+# `apt-get install -y podman` alone does not downgrade an already-installed
+# newer version, so the pin's Pin-Priority authorizes the downgrade and
+# --allow-downgrades permits apt to execute it.
+#
+# See #5733. Remove this pin once runner images ship crun >= 1.15
+# (podman 5.x's requirement) as standard.
+#
+# Usage:
+#   .github/scripts/install-podman.sh
+set -euo pipefail
+
+sudo install -d /etc/apt/preferences.d
+printf 'Package: podman\nPin: version 4.*\nPin-Priority: 1001\n' \
+  | sudo tee /etc/apt/preferences.d/podman-pin >/dev/null
+sudo apt-get update
+sudo apt-get install -y --allow-downgrades podman
+
+installed_version="$(podman --version)"
+case "${installed_version}" in
+  *"version 4."*) ;;
+  *)
+    echo "::error::Failed to pin podman to the 4.x series (see #5733); got: ${installed_version}"
+    exit 1
+    ;;
+esac
+
+echo "${installed_version}"

.github/workflows/functional-tests.yml

@@ -185,9 +185,7 @@ jobs:
 
       - name: Install Podman
         if: steps.changes.outputs.relevant != 'false'
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y podman
+        run: .github/scripts/install-podman.sh
 
       - name: Configure rootless Podman
         if: steps.changes.outputs.relevant != 'false'

action.yml

@@ -257,10 +257,7 @@ runs:
 
     - name: Install Podman
       shell: bash
-      run: |
-        sudo apt-get update
-        sudo apt-get install -y podman
-        podman --version
+      run: "$GITHUB_ACTION_PATH/.github/scripts/install-podman.sh"
 
     - name: Configure rootless Podman
       shell: bash

internal/scaffold/vendormanifest.go

@@ -153,6 +153,7 @@ var vendoredDefaultsInfraPaths = []string{
 	".github/actions/setup-gcp/action.yml",
 	".github/actions/validate-enrollment/action.yml",
 	".github/scripts/install-openshell.sh",
+	".github/scripts/install-podman.sh",
 	".github/scripts/openshell-version.sh",
 }