ci(build): ignore failing upload-artifacts step

Build steps are often failing with "ECONNRESET" errors due to
rate-limiting by github. We usually don't need/care about the
artifacts, so don't have to fail the build when the upload fails.

related to #502 and #actions/upload-artifact/issues/116

.github/workflows/build.yml

@@ -112,3 +112,4 @@ jobs:
           path: |
             build/zephyr/zmk.hex
             build/zephyr/zmk.uf2
+        continue-on-error: true