[CI] Bump GitHub Actions Runner to Ubuntu 20. (#10678)

* Bump GitHub Actions Runner to Ubuntu 20.

* Bump GitHub Actions Runner to Ubuntu 20 (2, license check).
diff --git a/.github/workflows/build-and-test-3.1.yml b/.github/workflows/build-and-test-3.1.yml
index 4af4b24..f8c4370 100644
--- a/.github/workflows/build-and-test-3.1.yml
+++ b/.github/workflows/build-and-test-3.1.yml
@@ -19,7 +19,7 @@
 
 jobs:
   license:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - name: Check License
@@ -27,7 +27,7 @@
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
   build-source:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     outputs:
       version: ${{ steps.dubbo-version.outputs.version }}
     steps:
@@ -82,7 +82,7 @@
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-18.04, windows-2019 ]
+        os: [ ubuntu-20.04, windows-2019 ]
         jdk: [ 8, 11, 17 ]
     env:
       DISABLE_FILE_SYSTEM_TEST: true
@@ -134,7 +134,7 @@
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-18.04, windows-2019 ]
+        os: [ ubuntu-20.04, windows-2019 ]
         jdk: [ 8, 11, 17 ]
     env:
       DISABLE_FILE_SYSTEM_TEST: true
@@ -169,7 +169,7 @@
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-18.04, windows-2019 ]
+        os: [ ubuntu-20.04, windows-2019 ]
         jdk: [ 8, 11, 17 ]
     env:
       DISABLE_FILE_SYSTEM_TEST: true
@@ -200,7 +200,7 @@
         uses: codecov/codecov-action@v1
 
   integration-test-prepare:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     env:
       JOB_COUNT: 3
     steps:
@@ -219,8 +219,8 @@
 
   integration-test-job:
     needs: [build-source, integration-test-prepare]
-    name: "Integration Test on ubuntu-18.04 (JobId: ${{matrix.job_id}})"
-    runs-on: ubuntu-18.04
+    name: "Integration Test on ubuntu-20.04 (JobId: ${{matrix.job_id}})"
+    runs-on: ubuntu-20.04
     timeout-minutes: 30
     env:
       JAVA_VER: 8
@@ -275,7 +275,7 @@
   integration-test-result:
     needs: [integration-test-job]
     if: always()
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     env:
       JAVA_VER: 8
     steps: