Update Github checkout action

Resolves node.js V12 deprecation warning.

.github/workflows/ci-docker.yml

@@ -7,7 +7,7 @@ jobs:
     name: Arch Linux (via Docker) CI
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
     - name: Test Action
       uses: ./util/ci/actions/archlinux-test
     - uses: actions/upload-artifact@v2

.github/workflows/ci-tests.yml

@@ -9,7 +9,7 @@ jobs:
       TZ: America/Los_Angeles
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
     - run: sudo apt-get update
     - name: Install additional dependencies
       run: sudo apt-get install -y gettext cmake libxslt-dev xsltproc ninja-build libboost-all-dev libgtk-3-dev guile-2.2-dev libgwengui-gtk3-dev libaqbanking-dev libofx-dev libdbi-dev libdbd-sqlite3 libwebkit2gtk-4.0-dev  googletest

.github/workflows/mac-tests.yaml

@@ -9,7 +9,7 @@ jobs:
       TZ: America/Los_Angeles
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
     - run: |
         echo "PATH=$PATH:$HOME/gnucash/inst/bin" >> $GITHUB_ENV
         echo "PREFIX=$HOME/gnucash/inst" >> $GITHUB_ENV