test: Fix cleanup in TestStoragePackages.testNfsMissingPackages
test: Fix cleanup in TestStoragePackages.testNfsMissingPackages

Re-enable /sbin/mount.nfs after the test ran.

Closes #13590
deryni/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,deryni/cockpit,moraleslazaro/cockpit,garrett/cockpit,deryni/cockpit,martinpitt/cockpit,cockpituous/cockpit,garrett/cockpit,martinpitt/cockpit,cockpituous/cockpit,cockpituous/cockpit,cockpituous/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,deryni/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,garrett/cockpit,martinpitt/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,cockpituous/cockpit,deryni/cockpit,garrett/cockpit,deryni/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,deryni/cockpit,moraleslazaro/cockpit,garrett/cockpit