fix(ci): remove Node 18 due to node-canvas installation issues

- per the in-line comment, there are some upstream issues in node-canvas that is causing installation to fail on Node 18
- made a TODO to add Node 18 back to the matrix once it's properly supported upstream

Author: agilgur5

.github/workflows/ci.yml

@@ -7,7 +7,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        node-version: [14.x, 16.x, 18.x] # LTS Node: https://nodejs.org/en/about/releases/
+        # TODO: add back Node 18 once node-canvas is properly supported: https://github.com/Automattic/node-canvas/issues/2025
+        node-version: [14.x, 16.x] # LTS Node: https://nodejs.org/en/about/releases/
         os: [ubuntu-latest, windows-latest, macOS-latest]
 
     steps: