bin/_docker.sh: Fix shellcheck issues (#4433)

Signed-off-by: Joakim Roubert <joakimr@axis.com>

.github/workflows/static_checks.yml

@@ -80,7 +80,6 @@ jobs:
       run: |
         find ./bin -type f \
         ! -name docker-build-proxy \
-        ! -name _docker.sh \
         ! -name fmt \
         ! -name lint \
         ! -name _log.sh \

bin/_docker.sh

@@ -1,3 +1,5 @@
+#!/bin/bash
+
 set -eu
 
 bindir=$( cd "${BASH_SOURCE[0]%/*}" && pwd )
@@ -33,8 +35,6 @@ docker_build() {
     file=$1
     shift
 
-    extra="$@"
-
     output=/dev/null
     if [ -n "$DOCKER_TRACE" ]; then
         output=/dev/stderr
@@ -42,11 +42,11 @@ docker_build() {
 
     rootdir=$( cd "$bindir"/.. && pwd )
 
-    log_debug "  :; docker build $rootdir -t $repo:$tag -f $file $extra"
+    log_debug "  :; docker build $rootdir -t $repo:$tag -f $file $*"
     docker build "$rootdir" \
         -t "$repo:$tag" \
         -f "$file" \
-        $extra \
+        "$@" \
         > "$output"
 
     echo "$repo:$tag"