CI: Bump ubuntu to 24.04

Ubuntu 20.04 fails to build with protoc 3.6.1.3.
app_processes.proto:29:14: Explicit 'optional' labels are disallowed in the Proto3 syntax.
To define 'optional' fields in Proto3, simply remove the 'optional' label, as fields are 'optional' by default.

Ubuntu 22.04 fails to build with protoc 3.12.4.
app_processes.proto: This file contains proto3 optional fields, but --experimental_allow_proto3_optional was not set.

clang-14 in Ubuntu fails to build.
chrono:2360:48: error: call to consteval function 'std::chrono::hh_mm_ss::_S_fractional_width' is not a constant expression
chrono:2360:48: note: undefined function '_S_fractional_width' cannot be used in a constant expression

.github/workflows/build.yml

@@ -68,12 +68,12 @@ jobs:
           - os: "archlinux:base"
             pkgs: clang
             env1: "CC=clang CXX=clang++"
-          - os: "ubuntu:20.04"
+          - os: "ubuntu:24.04"
             pkgs: "gcc-10 g++-10"
             env1: "CC=gcc-10 CXX=g++-10"
-          - os: "ubuntu:20.04"
-            pkgs: "clang-11 libstdc++-10-dev"
-            env1: "CC=clang-11 CXX=clang++-11"
+          - os: "ubuntu:24.04"
+            pkgs: "clang-15 libstdc++-10-dev"
+            env1: "CC=clang-15 CXX=clang++-15"
           - os: "alpine"
             pkgs: "gcc"
             env1: "CC=gcc CXX=g++"