ci: Improve the linux-cross-arm configuration

Run the tests on arm, too, and print the version of the compiler
used for aarch64 (even though it's probably in practice always
the same as for arm).

.github/workflows/build.yaml

@@ -104,9 +104,11 @@ jobs:
       - run: sudo apt-get update -qq
       - run: sudo apt-get install -qq g++-arm-linux-gnueabihf g++-aarch64-linux-gnu qemu-user
       - run: arm-linux-gnueabihf-g++ --version
+      - run: aarch64-linux-gnu-g++ --version
       - run: make gmp-bootstrap
       - run: make gtest-bootstrap
       - run: CFLAGS=-Werror make -j$(nproc) ARCH=armv7 CC=arm-linux-gnueabihf-gcc CXX=arm-linux-gnueabihf-g++
+      - run: qemu-armhf -L /usr/arm-linux-gnueabihf/ ./codec_unittest
       - run: CFLAGS=-Werror make clean
       - run: CFLAGS=-Werror make -j$(nproc) ARCH=aarch64 CC=aarch64-linux-gnu-gcc CXX=aarch64-linux-gnu-g++
       - run: qemu-aarch64 -L /usr/aarch64-linux-gnu/ ./codec_unittest