`test/cases/ostree.sh`: line 261: UPGRADE_PATH: unbound variable

[thozza]

The test case log contains an error when the test fails:

...
ssh: connect to host 192.168.100.50 port 22: No route to host
ssh: connect to host 192.168.100.50 port 22: No route to host
ssh: connect to host 192.168.100.50 port 22: No route to host
ssh: connect to host 192.168.100.50 port 22: No route to host
ssh: connect to host 192.168.100.50 port 22: No route to host
[2022-03-09T16:59:32-05:00] Checking for test result
[2022-03-09T16:59:32-05:00] ❌ Failed
[2022-03-09T16:59:32-05:00] 🧼 Cleaning up
Domain osbuild-composer-ostree-test-c30b453a-08cc-40ab-9527-3625d2f5af9c destroyed
Domain osbuild-composer-ostree-test-c30b453a-08cc-40ab-9527-3625d2f5af9c has been undefined
/usr/libexec/tests/osbuild-composer/ostree.sh: line 261: UPGRADE_PATH: unbound variable
...

Example: https://gitlab.com/osbuild/ci/osbuild-composer/-/jobs/2184482968