Try using west.yml file instead.

.gitlab-ci.yml

@@ -3,8 +3,7 @@ build:
   image: zephyrprojectrtos/zephyr-build
 
   before_script:
-    - west init -m https://github.com/petejohanson/zephyr --mr driver-kscan-gpio-matrix-first-pass
-    - west update .
+    - west init
 
   script:
     - west build -b nucelo_wb55rg -- -DSHIELD=petejohanson_handwire

west.yml

@@ -0,0 +1,13 @@
+manifest:
+  remotes:
+    - name: zephyrproject-rtos
+      url-base: https://github.com/zephyrproject-rtos
+    - name: petejohanson
+      url-base: https://github.com/petejohanson
+  projects:
+    - name: zephyr
+      remote: petejohanson
+      revision: driver-kscan-gpio-matrix-first-pass
+      import: true
+  self:
+    path: zmk