[FLINK-36923] Bump Flink version to 1.20.0, adapt CI workflow

Author: lvyanquan

.github/workflows/push_pr.yml

@@ -28,7 +28,7 @@ jobs:
   compile_and_test:
     strategy:
       matrix:
-        flink: [ 1.18.1, 1.19.1 ]
+        flink: [ 1.20.0 ]
         jdk: [ '8, 11' ]
     uses: apache/flink-connector-shared-utils/.github/workflows/ci.yml@ci_utils
     with:

.github/workflows/weekly.yml

@@ -30,10 +30,7 @@ jobs:
     strategy:
       matrix:
         flink_branches: [{
-          flink: 1.19-SNAPSHOT,
-          branch: main
-        }, {
-          flink: 1.18-SNAPSHOT,
+          flink: 1.20-SNAPSHOT,
           branch: main
         }, {
           flink: 1.19.1,

pom.xml

@@ -52,7 +52,7 @@ under the License.
 	</scm>
 
 	<properties>
-		<flink.version>1.18.1</flink.version>
+		<flink.version>1.20.0</flink.version>
 
 		<scala.binary.version>2.12</scala.binary.version>
 		<scala.version>2.12.7</scala.version>