tests: fix ctest path in build scripts

The scripts cd into build/ before running make, so --test-dir build
resolved to build/build/. Drop --test-dir and let ctest run in the
current directory instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: andy5995

mk/linux/build-mg.sh

@@ -377,7 +377,7 @@ else
 
         if [ $RUN_TESTS = 1 ]; then
             echo "==================> Running unit tests... <=================================="
-            ctest --test-dir build --output-on-failure
+            ctest --output-on-failure
             if [ $? -ne 0 ]; then
               echo 'ERROR: Tests failed.' >&2; exit 3
             fi

mk/macos/build-mg.sh

@@ -269,7 +269,7 @@ else
 
 		if [ "$RUN_TESTS" -eq "1" ]; then
 			echo "==================> Running unit tests... <=================================="
-			ctest --test-dir build --output-on-failure
+			ctest --output-on-failure
 			if [ "$?" -ne "0" ]; then echo 'ERROR: Tests failed.' >&2; exit 3; fi
 		fi
 	fi