[CI] Allow use of Node 16

We build and test on our Docker image, which is based on the ASWF
VFX Reference Platform 2022 image, whose glibc version is rather old.
This makes it incompatible with Node 20. We have been holding back the
version of `actions/checkout` to ensure Node 16 was still used. However,
GitHub have started forcing Node 20 regardless. See
https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/

That link gives a way to buy more time on Node 16 via a
`ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION` env var.

Signed-off-by: David Feltell <[email protected]>

Author: feltech

.github/workflows/test.yml

@@ -7,6 +7,13 @@ name: Test
 on:
   pull_request:
 
+env:
+  # Buy some more time to use the deprecated Node 16 (needed for GLIBC
+  # version)
+  # Upgrading to the CY23 Docker images will solve this longer term. See
+  # https://github.com/OpenAssetIO/OpenAssetIO/issues/984#issuecomment-2210792734
+  ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true
+
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true