package/rtl_433: do not leak Buildroot git info

The CMake build system has logic to detect the git repo info and include it
in the version output.  This unfortunately gets confused and adds the git
info of the Buildroot repository when building inside the repo:

-- Found Git version: refs/heads/rtl_433-25.02 commit a367362af00ed349915b0b4496ebeb9910fc86e4                                 from 2025-09-21T20:07:58+0200
-- Using Git version tag: 2025.08-283-ga367362af0 on rtl_433-25.02 at 202509212007

rtl_433 -V
rtl_433 version 2025.08-283-ga367362af0 branch rtl_433-25.02 at 202509212007 inputs file rtl_tcp RTL-SDR

Pass GIT_DIR=.  to the configure step similar to how it is already done for
the build step to disable this.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/rtl_433/rtl_433.mk

@@ -18,6 +18,9 @@ RTL_433_CONF_OPTS = \
 	-DBUILD_TESTING_ANALYZER=OFF \
 	-DENABLE_SOAPYSDR=OFF
 
+# do not include Buildroot git info in version output
+RTL_433_CONF_ENV = GIT_DIR=.
+
 ifeq ($(BR2_PACKAGE_LIBRTLSDR),y)
 RTL_433_DEPENDENCIES += librtlsdr
 RTL_433_CONF_OPTS += -DENABLE_RTLSDR=ON