docker: Fix line continuation after 986847858c

Dockerfile.dev

@@ -148,8 +148,8 @@ RUN cd test && \
 
 RUN cd test && \
     for arch in $TOOLCHAIN_ARCHS; do \
-        case $arch in
-        arm64ec) continue ;;
-        esac
+        case $arch in \
+        arm64ec) continue ;; \
+        esac; \
         cp $TOOLCHAIN_PREFIX/$arch-w64-mingw32/bin/*.dll $arch || exit 1; \
     done