Bump rhel to gcc13, to avoid gcc12 warnings in openair1

docker/Dockerfile.build.rhel9

@@ -38,7 +38,7 @@ COPY . .
 RUN /bin/sh oaienv && \ 
     cd cmake_targets && \
     mkdir -p log && \
-    scl enable gcc-toolset-12 "\
+    scl enable gcc-toolset-13 "\
     CXXFLAGS='-Werror -fstack-protector-strong' CFLAGS='-Werror -fstack-protector-strong' ./build_oai -c --ninja \
       --eNB --gNB --RU --UE --nrUE \
       --build-e2 --cmake-opt -DXAPP_MULTILANGUAGE=OFF --cmake-opt \
@@ -54,7 +54,7 @@ RUN /bin/sh oaienv && \
 ## Build FlexRIC for SM Models
 RUN mkdir -p openair2/E2AP/flexric/build && \
     cd openair2/E2AP/flexric/build && \
-    scl enable gcc-toolset-12 "\
+    scl enable gcc-toolset-13 "\
     cmake -GNinja -DCMAKE_BUILD_TYPE=Release \
           -DXAPP_MULTILANGUAGE=OFF \
           -DKPM_VERSION=$KPM_VERSION \