test-manifest: Update to reference release/ncs-v2.6-branch-NCSIDB-1718

Update test-manifest to reference the branch
release/ncs-v2.6-branch-NCSIDB-1718 for test_nrf.

Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: cvinayak

test-manifests/99-default-test-nrf.yml

@@ -11,7 +11,7 @@ manifest:
     - name: test_nrf
       remote: ncs-test
       repo-path: test-fw-nrfconnect-nrf
-      revision: v2.6-branch
+      revision: release/ncs-v2.6-branch-NCSIDB-1718
       import:
         name-blocklist: [sdk-nrf]
       userdata: