chore: install cosign only if needed

Signed-off-by: Bence Csati <bence.csati@axoflow.com>

Author: csatib02

.github/workflows/artifacts.yaml

@@ -94,6 +94,7 @@ jobs:
 
       - name: Set up Cosign
         uses: sigstore/cosign-installer@dc72c7d5c4d10cd6bcb8cf6e3fd625a9e5e537da # v3.7.0
+        if: inputs.publish
 
       - name: Set image name
         id: image-name
@@ -275,6 +276,7 @@ jobs:
 
       - name: Set up Cosign
         uses: sigstore/cosign-installer@dc72c7d5c4d10cd6bcb8cf6e3fd625a9e5e537da # v3.7.0
+        if: inputs.publish && inputs.release
 
       - name: Set chart name
         id: chart-name
@@ -435,6 +437,7 @@ jobs:
 
       - name: Set up Cosign
         uses: sigstore/cosign-installer@dc72c7d5c4d10cd6bcb8cf6e3fd625a9e5e537da # v3.7.0
+        if: inputs.publish && inputs.release
 
       - name: Set chart name
         id: chart-name