Fix CI: pin .NET SDK to 8.0 and fail on build errors

Add global.json to pin the .NET SDK to 8.0.x, preventing CI runners
with .NET 10 pre-installed from using the wrong compiler (which breaks
Docxodus due to List<T>.Reverse() vs LINQ Reverse() resolution).

Also fix build_differ.py run_command() to raise on non-zero exit codes
instead of silently continuing past build failures.

Author: JSv4

build_differ.py

@@ -26,11 +26,14 @@ def get_version():
 
 def run_command(command):
     """
-    Runs a shell command and prints its output.
+    Runs a shell command and prints its output. Raises on non-zero exit code.
     """
     process = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
     for line in process.stdout:
         print(line.decode().strip())
+    process.wait()
+    if process.returncode != 0:
+        raise RuntimeError(f"Command failed with exit code {process.returncode}: {command}")
 
 
 def compress_files(source_dir, target_file):

global.json

@@ -0,0 +1,6 @@
+{
+  "sdk": {
+    "version": "8.0.0",
+    "rollForward": "latestFeature"
+  }
+}