Use npm instead of yarn for GitHub Actions

Author: Adrián Bolonio

.github/workflows/axe.yml

@@ -12,7 +12,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [14.x, 16.x]
+        node-version: [16.x]
 
     steps:
       - uses: actions/checkout@v3

.github/workflows/pa11y.yml

@@ -12,7 +12,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [14.x, 16.x]
+        node-version: [16.x]
 
     steps:
       - uses: actions/checkout@v3

.github/workflows/unit-test.yml

@@ -12,7 +12,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [14.x, 16.x]
+        node-version: [16.x]
 
     steps:
       - uses: actions/checkout@v3