Update Ubuntu runner image to get later SWIG

We need version 4.2.0 to build ABI3 Python bindings. Ubuntu has max version
numbers for packages tied to the Ubuntu version, so upgrading Ubuntu is probably
the easiest fix here. The GH runner readme says it has SWIG 4.2.0:
https://github.com/actions/runner-images/blob/main/images/ubuntu/Ubuntu2404-Readme.md

Improve the SWIG version error by printing the required and found SWIG versions.

.github/workflows/build.yml

@@ -1,6 +1,6 @@
 # Build, test and upload executables to GitHub
 # depends on pre-installed software; see image definitions:
-#  - https://github.com/actions/runner-images/blob/main/images/linux/Ubuntu2004-Readme.md
+#  - https://github.com/actions/runner-images/blob/main/images/linux/Ubuntu2404-Readme.md
 #  - https://github.com/actions/runner-images/blob/main/images/macos/macos-12-Readme.md
 # We use these tools from the runner images: git, gcc/XCode/MSVC, swig, Tcl/Tk on MacOS, pkg-config
 
@@ -28,7 +28,8 @@ jobs:
       fail-fast: false
       matrix:
         os: [
-          ubuntu-latest,
+          # Use v24 beta for now to get newer SWIG; TODO: change back to ubuntu-latest once it points to v24
+          ubuntu-24.04,
           # latest available X86_64 target
           macos-12,
           # latest is ARM

Core/ClientSMLSWIG/Python/SConscript

@@ -85,7 +85,7 @@ if "SOAR_PYTHON_ABI3" in env["ENV"]:
         clone.Append(CPPDEFINES = { 'Py_LIMITED_API': api_version })
     else:
         print("'Requested building Python SML bindings with Python's Limited API, "
-              "while SWIG does not support it, aborting.'", file=sys.stderr)
+              f"but SWIG does not support it (need 4.2.0, have {'.'.join(env['SWIG_VERSION'])}); aborting.'", file=sys.stderr)
         Exit(1)
 else:
     print("SOAR_PYTHON_ABI3 not defined, building Python SML bindings with full (less portable) Python API...")