.gitlab-ci.yml: add raspberrypi4_defconfig

fa1ce849f3061fab282aa78ebff3cc30abb08f4f added raspberrypi4_defconfig
but forgot to update .gitlab-ci.yml.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

.gitlab-ci.yml

@@ -298,6 +298,7 @@ raspberrypi2_defconfig: { extends: .defconfig }
 raspberrypi3_64_defconfig: { extends: .defconfig }
 raspberrypi3_defconfig: { extends: .defconfig }
 raspberrypi3_qt5we_defconfig: { extends: .defconfig }
+raspberrypi4_defconfig: { extends: .defconfig }
 raspberrypi_defconfig: { extends: .defconfig }
 riotboard_defconfig: { extends: .defconfig }
 rock64_defconfig: { extends: .defconfig }