build: Upgrade to Node 20 (#47)

### Description

- Regenerated `package-lock.json` with node `v20` and NPM `10`.
- Updated `.nvmrc` to `v20`
- Updated the `lockfile` version check workflow 

Second step in the Node 20 upgrade process, See [the tracking
issue](#45) for
further information.

.github/workflows/ci.yml

@@ -14,7 +14,6 @@ jobs:
     strategy:
       matrix:
         node: [18, 20]
-    continue-on-error: ${{ matrix.node == 20 }}
     steps:
     - name: Checkout
       uses: actions/checkout@v2

.github/workflows/lockfileversion-check.yml

@@ -10,4 +10,4 @@ on:
 
 jobs:
   version-check:
-    uses: openedx/.github/.github/workflows/lockfile-check.yml@master
+    uses: openedx/.github/.github/workflows/lockfileversion-check-v3.yml@master

.nvmrc

@@ -1 +1 @@
-18
+20