ci: fix OpenURI::HTTPError: 401 Unauthorized error (#5206)

**Which issue(s) this PR fixes**: 

Fixes #

**What this PR does / why we need it**: 

With #5169,  it introduced rake task to backport Pull requests, but
it needs to pass GITHUB_TOKEN for internal script.

**Docs Changes**:

N/A

**Release Note**: 

N/A

---------

Signed-off-by: Kentaro Hayashi <[email protected]>

Author: kenhys

.github/workflows/backport.yml

@@ -1,4 +1,4 @@
-name: Backport
+name: Backport Pull Requests
 
 on:
   schedule:
@@ -22,15 +22,17 @@ jobs:
         ruby-version: ['3.4']
         task: ['backport:v1_16', 'backport:v1_19']
 
-    name: Backport PR on ${{ matrix.os }}
+    name: Backport PR ( ${{ matrix.task }} )
     steps:
       - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
       - name: Set up Ruby
         uses: ruby/setup-ruby@ac793fdd38cc468a4dd57246fa9d0e868aba9085 # v1.270.0
         with:
           ruby-version: ${{ matrix.ruby-version }}
           bundler-cache: true
-      - name: Run backport task
+      - name: Run backport task ( ${{ matrix.task }} )
         shell: bash
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           bundle exec rake ${{ matrix.task }}