Add missing buildtool_depend on git (ros2#37)

This vendor package uses git to fetch sources for other packages. It should declare a dependency on that build tool.

This should address the current cause of RPM build failures for RHEL: https://build.ros2.org/view/Rbin_rhel_el864/job/Rbin_rhel_el864__mcap_vendor__rhel_8_x86_64__binary/

Signed-off-by: Scott K Logan <logans@cottsay.net>
Signed-off-by: James Smith <james@foxglove.dev>

mcap_vendor/package.xml

@@ -8,6 +8,7 @@
   <license>Apache License 2.0</license>
 
   <buildtool_depend>ament_cmake</buildtool_depend>
+  <buildtool_depend>git</buildtool_depend>
 
   <test_depend>ament_cmake_clang_format</test_depend>
   <test_depend>ament_lint_auto</test_depend>