Use vfs storage driver for building container images

Some of our Forgejo Runners use tmpfs, which causes buildah to fail:
 * https://stackoverflow.com/questions/72651641
 * 9665efd712/troubleshooting.md (6-rootless-buildah-build-fails-when-using-overlayfs)

Instead of switching to overlayfs which may or may not work depending on
kernel module being loaded, we will use vfs because it always works.
Performance loss is not critical in our usage scenario

Signed-off-by: Vitaliy Potyarkin <v.potyarkin@yadro.com>

.forgejo/workflows/build.yml

@@ -14,6 +14,8 @@ jobs:
           - openjdk-11-maven-3.8.6
           - python-3.11
           - python-3.13
+    env:
+      STORAGE_DRIVER: vfs
     steps:
       - name: Clone git repo
         uses: actions/checkout@v3
@@ -26,7 +28,11 @@ jobs:
         id: changed
 
       - name: Install Buildah
-        run: apt update; apt install -y buildah
+        run: |-
+          apt update; apt install -y buildah
+
+          # STORAGE_DRIVER variable is ignored if this file does not exist
+          touch /etc/containers/storage.conf
         if: >-
           github.event_name == 'workflow_dispatch'
           || steps.changed.outputs.any_changed == 'true'