[hotfix] Fix building status badge in README as workflow files have been refactored (apache#3807)

* [hotfix] Fix building status badge in README as workflow files have been refactored

Signed-off-by: yuxiqian <34335406+yuxiqian@users.noreply.github.com>

* fix: rename workflow files to `flink_cdc_ci` / `flink_cdc_ci_nightly`

As they're not strictly tied to specific JDK versions.

Signed-off-by: yuxiqian <34335406+yuxiqian@users.noreply.github.com>

---------

Signed-off-by: yuxiqian <34335406+yuxiqian@users.noreply.github.com>

Author: yuxiqian

.github/workflows/flink_cdc_java_8.yml .github/workflows/flink_cdc_ci.yml.github/workflows/flink_cdc_java_8.yml renamed to .github/workflows/flink_cdc_ci.yml

@@ -8,8 +8,11 @@
 <a href="https://github.com/apache/flink-cdc/releases" target="_blank">
     <img src="https://img.shields.io/github/v/release/apache/flink-cdc?color=yellow" alt="Release">
 </a>
-<a href="https://github.com/apache/flink-cdc/actions/workflows/flink_cdc.yml" target="_blank">
-    <img src="https://img.shields.io/github/actions/workflow/status/apache/flink-cdc/flink_cdc.yml?branch=master" alt="Build">
+<a href="https://github.com/apache/flink-cdc/actions/workflows/flink_cdc_ci.yml" target="_blank">
+    <img src="https://img.shields.io/github/actions/workflow/status/apache/flink-cdc/flink_cdc_ci.yml?branch=master" alt="Build">
+</a>
+<a href="https://github.com/apache/flink-cdc/actions/workflows/flink_cdc_ci_nightly.yml" target="_blank">
+    <img src="https://img.shields.io/github/actions/workflow/status/apache/flink-cdc/flink_cdc_ci_nightly.yml?branch=master&label=nightly" alt="Nightly Build">
 </a>
 <a href="https://github.com/apache/flink-cdc/tree/master/LICENSE" target="_blank">
     <img src="https://img.shields.io/static/v1?label=license&message=Apache License 2.0&color=white" alt="License">