CI: disable persist-credentials for actions/checkout

It is a possible security issue.
We do not want to persist credentials in the repo and thus exposing those
to further steps.

References:

* actions/checkout#485 (comment)
* azat/chdig#67

.github/workflows/ci.yml

@@ -18,6 +18,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
+        with:
+          persist-credentials: false
 
       - name: Set up Ruby 2.7
         uses: ruby/setup-ruby@v1
@@ -41,6 +43,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
+        with:
+          persist-credentials: false
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}

.github/workflows/release.yml

@@ -11,6 +11,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
+        with:
+          persist-credentials: false
 
       - name: Set up Ruby 2.7
         uses: ruby/setup-ruby@v1