ci: Fix OWNER variable in netperf workflow for push events

The network performance workflow has a step named `vars` which
determines an appropriate value for an environment variable named OWNER.
This environment variable is added as a label into the GKE cluster the
workflow creates. This commit fixes a bug where, if the branch the
workflow is ran from contained a forward-slash, cluster creation would
fail, as GKE cluster labels cannot contain forward slashes.

Signed-off-by: Ryan Drew <ryan.drew@isovalent.com>

.github/workflows/net-perf-gke.yaml

@@ -151,7 +151,7 @@ jobs:
           else
             SHA="${{ github.sha }}"
             OWNER="${{ github.ref_name }}"
-            OWNER="${OWNER/./-}"
+            OWNER="${OWNER//[.\/]/-}"
           fi
 
           CILIUM_INSTALL_DEFAULTS="--chart-directory=install/kubernetes/cilium \