CI: bump actions/checkout action to v3

Bump actions/checkout action to v3 on every workflow to mute node
deprecation warning.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

.github/workflows/kernel.yml

@@ -28,7 +28,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Set lower case owner name
         id: lower_owner
@@ -83,30 +83,30 @@ jobs:
 
     steps:
       - name: Checkout master directory
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           path: openwrt
 
       - name: Checkout packages feed
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           repository: openwrt/packages
           path: openwrt/feeds/packages
 
       - name: Checkout luci feed
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           repository: openwrt/luci
           path: openwrt/feeds/luci
 
       - name: Checkout routing feed
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           repository: openwrt/routing
           path: openwrt/feeds/routing
 
       - name: Checkout telephony feed
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           repository: openwrt/telephony
           path: openwrt/feeds/telephony