chore: upgrade ubuntu to latest version in CI

[Revolyssup]

Description

In light of the deprecation of 20.04 - actions/runner-images#11101

Fixes # (issue)
Upgrading ubuntu

Checklist

Other changes to keep compatibility with Ubuntu latest.

1. The dubbo backend script needs java8 and after upgrade the java version goes up. So change has been made to stick it to java 8.
2. Changing cli.yaml - Ubuntu 20.04’s default umask allowed files to be created with 644 permissions by default, so even when the script overwrote config.yaml, the file remained readable by all users. Newer Ubuntu versions tightened security defaults, leading to 640/600 permissions, which broke APISIX’s ability to read config.yaml. So the umask is set to 022 so new files are created by default with 644 permission.

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)