README: upgrade GitHub action in examples (#950)

Upgrade actions/checkout from v2 to v3 in GitHub actions examples.

Author: dolmen

README.md

@@ -68,7 +68,7 @@ jobs:
       GO111MODULE: on
     steps:
       - name: Checkout Source
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Run Gosec Security Scanner
         uses: securego/gosec@master
         with:
@@ -98,7 +98,7 @@ jobs:
       GO111MODULE: on
     steps:
       - name: Checkout Source
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Run Gosec Security Scanner
         uses: securego/gosec@master
         with: