Add clang-20 into all relevant 24.04 tests and disable clang-18.

Author: sobomax

.github/workflows/rtpproxy_ci.yml

@@ -141,10 +141,11 @@ jobs:
           compiler: 'clang-16'
         - os: 24.04
           compiler: 'clang-17'
-        - os: 24.04
-          compiler: 'clang-18'
         - os: 24.04
           compiler: 'clang-19'
+        - os: 24.04
+          compiler: 'clang-20'
+
     steps:
     - uses: actions/checkout@v4
       with:
@@ -215,10 +216,10 @@ jobs:
           compiler: 'clang-16'
         - os: 24.04
           compiler: 'clang-17'
-        - os: 24.04
-          compiler: 'clang-18'
         - os: 24.04
           compiler: 'clang-19'
+        - os: 24.04
+          compiler: 'clang-20'
 
     steps:
     - uses: actions/checkout@v4
@@ -289,10 +290,10 @@ jobs:
           compiler: 'clang-16'
         - os: 24.04
           compiler: 'clang-17'
-        - os: 24.04
-          compiler: 'clang-18'
         - os: 24.04
           compiler: 'clang-19'
+        - os: 24.04
+          compiler: 'clang-20'
 
     steps:
     - uses: actions/checkout@v4