CI : Continue using Node16 for actions

Actions are now run on Node20 by default, but this requires glibc >=2.28 so actions no longer run in our CentOS 7 build container.

Setting ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true allows us to continue using Node16 for the near future, but support for this may be removed in October...

https://github.blog/changelog/2024-05-17-updated-dates-for-actions-runner-using-node20-instead-of-node16-by-default/

Author: murraystevenson

.github/workflows/main.yml

@@ -86,6 +86,12 @@ jobs:
 
     container: ${{ matrix.containerImage }}
 
+    env:
+      # GitHub have moved to running actions on Node20, which prevents them from
+      # running on CentOS 7. The below allows actions to continue running on Node16
+      # until October.
+      ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true
+
     steps:
 
     - uses: actions/checkout@v2