fix(build): move mavsdk_tests target out of gazebo-classic cmake file

The ExternalProject_Add(mavsdk_tests ...) lived at the bottom of
sitl_targets_gazebo-classic.cmake, outside the if(gazebo_FOUND) gate
and with a comment noting it doesn't depend on sitl_gazebo. Historical
artifact: mavsdk_tests is a black-box MAVLink test driver that talks
to a running PX4 over UDP, and works against any simulator backend
(sitl_gazebo-classic, gz, sih, jmavsim, ...).

With CI moving from classic Gazebo to SIH, the misplacement becomes
actively misleading. Pull the block into a new top-level
cmake/mavsdk_tests.cmake and include it from CMakeLists.txt under the
existing posix-only block, so the dependency graph reflects what is
actually true.

Behavior is unchanged: target is EXCLUDE_FROM_ALL, only built on
demand via `make mavsdk_tests` or `make tests_integration`.

CMakeLists.txt

@@ -360,6 +360,11 @@ if(${PX4_PLATFORM} STREQUAL "posix")
 	if (NOT CMAKE_INSTALL_PREFIX)
 		set(CMAKE_INSTALL_PREFIX "/usr" CACHE PATH "Install path prefix" FORCE)
 	endif()
+
+	# mavsdk integration tests — defined as an ExternalProject_Add target;
+	# EXCLUDE_FROM_ALL, so only built when explicitly requested
+	# (e.g. `make mavsdk_tests` or `make tests_integration`).
+	include(mavsdk_tests)
 endif()
 
 include(ccache)

cmake/mavsdk_tests.cmake

@@ -0,0 +1,49 @@
+############################################################################
+#
+# Copyright (c) 2026 PX4 Development Team. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in
+#    the documentation and/or other materials provided with the
+#    distribution.
+# 3. Neither the name PX4 nor the names of its contributors may be
+#    used to endorse or promote products derived from this software
+#    without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+# OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+############################################################################
+
+# mavsdk_tests is a black-box MAVLink integration-test driver that talks to a
+# running PX4 over UDP. It does not depend on any specific simulator backend
+# (sitl_gazebo-classic, gz, sih, jmavsim, ...) — it just needs a PX4 binary
+# to be running. Defined here at the top level rather than under any sitl
+# backend file so the dependency graph is honest.
+include(ExternalProject)
+ExternalProject_Add(mavsdk_tests
+	SOURCE_DIR ${PX4_SOURCE_DIR}/test/mavsdk_tests
+	CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
+	BINARY_DIR ${PX4_BINARY_DIR}/mavsdk_tests
+	INSTALL_COMMAND ""
+	USES_TERMINAL_CONFIGURE true
+	USES_TERMINAL_BUILD true
+	EXCLUDE_FROM_ALL true
+	BUILD_ALWAYS 1
+)

src/modules/simulation/simulator_mavlink/sitl_targets_gazebo-classic.cmake

@@ -247,16 +247,3 @@ if(gazebo_FOUND)
 	add_custom_target(gazebo-classic DEPENDS gazebo-classic_iris) # alias
 	add_custom_target(gazebo DEPENDS gazebo-classic_iris) # alias
 endif()
-
-# mavsdk tests DO NOT depend on sitl_gazebo
-include(ExternalProject)
-ExternalProject_Add(mavsdk_tests
-	SOURCE_DIR ${PX4_SOURCE_DIR}/test/mavsdk_tests
-	CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
-	BINARY_DIR ${PX4_BINARY_DIR}/mavsdk_tests
-	INSTALL_COMMAND ""
-	USES_TERMINAL_CONFIGURE true
-	USES_TERMINAL_BUILD true
-	EXCLUDE_FROM_ALL true
-	BUILD_ALWAYS 1
-)