build: docker run: make "-it" flags conditional on tty being available

from https://stackoverflow.com/a/69088164

I am trying to run the build.sh scripts directly on a cirrus CI runner, and "docker run -it" is erroring due to lack of a tty.

contrib/build-linux/sdist/build.sh

@@ -46,6 +46,12 @@ else
     info "not doing fresh clone."
 fi
 
+DOCKER_RUN_FLAGS=""
+if sh -c ": >/dev/tty" >/dev/null 2>/dev/null; then
+    info "/dev/tty is available and usable"
+    DOCKER_RUN_FLAGS="-it"
+fi
+
 info "building binary..."
 # check uid and maybe chown. see #8261
 if [ ! -z "$ELECBUILD_COMMIT" ] ; then  # fresh clone (reproducible build)
@@ -54,7 +60,7 @@ if [ ! -z "$ELECBUILD_COMMIT" ] ; then  # fresh clone (reproducible build)
         sudo chown -R 1000:1000 "$FRESH_CLONE"
     fi
 fi
-docker run -it \
+docker run $DOCKER_RUN_FLAGS \
     --name electrum-sdist-builder-cont \
     -v "$PROJECT_ROOT_OR_FRESHCLONE_ROOT":/opt/electrum \
     --rm \