Remove CentOS 7 and Ubuntu 18.04 from ContinuousIntegration.md.

Add Ubuntu 24.04.

Author: rjmansfield

docs/ContinuousIntegration.md

@@ -161,10 +161,9 @@ You can also build a toolchain for a specific Linux distribution
 Distro         | Comment                                          | Check Status
 -------------- | ------------------------------------------------ | ----------------------------------------------
 UBI9           | @swift-ci Please Build Toolchain UBI9            | Swift Build Toolchain UBI9 (x86_64)
-CentOS 7       | @swift-ci Please Build Toolchain CentOS 7        | Swift Build Toolchain CentOS 7 (x86_64)
-Ubuntu 18.04   | @swift-ci Please Build Toolchain Ubuntu 18.04    | Swift Build Toolchain Ubuntu 18.04 (x86_64)
 Ubuntu 20.04   | @swift-ci Please Build Toolchain Ubuntu 20.04    | Swift Build Toolchain Ubuntu 20.04 (x86_64)
 Ubuntu 22.04   | @swift-ci Please Build Toolchain Ubuntu 22.04    | Swift Build Toolchain Ubuntu 22.04 (x86_64)
+Ubuntu 24.04   | @swift-ci Please Build Toolchain Ubuntu 24.04    | Swift Build Toolchain Ubuntu 24.04 (x86_64)
 Amazon Linux 2 | @swift-ci Please Build Toolchain Amazon Linux 2  | Swift Build Toolchain Amazon Linux 2 (x86_64)
 
 ### Build and Test Stdlib against Snapshot Toolchain