922 Bump actions/checkout version in GHA workflows

#922

[author: gonzaponte]

The current version issues the following warning:

```
The following actions uses node12 which is deprecated and will be
forced to run on node16: actions/checkout@v2.
For more info:
https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/
```

Bumping to the latest version seems to get rid of it.

[reviewer: jwaiton]

Good change, we move from node16 to node20 with checkout@v4. From
reading https://github.com/actions/checkout/releases changelogs from
v2 -> v3 -> v4, it seems like there are no backwards compatibility
issues and the tests execute as expected.

There may be more complex behaviour in the differences between node16
& 20 but I can't find anything significant in documentation that warns
of this, or complaints online of said incompatibilities between
versions. Again, the tests run as expected looking at the output so
I'm happy.

.github/workflows/check_db_calibration.yml

@@ -21,7 +21,7 @@ jobs:
         python-version: [3.8]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - id: files
       uses: jitterbit/get-changed-files@v1
     - name: Set up Python ${{ matrix.python-version }}

.github/workflows/test_suite.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ${{ matrix.platform }}
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Get LFS files
       run: git lfs pull
     # - name: Fix Conda permissions on macOS