Correct folder name in build taskfile

A copy/paste error resulted in the same folder name being used for the Linux ARM 64-bit build as for the Linux ARM v6
build. Although that did not cause any noticeable problems in this project's usage, it can in others. For example:

```
mkdir: cannot create directory ‘serial-monitor_linux_arm_6’: File exists
task: Failed to run task "dist:all": task: Failed to run task "dist:Linux_ARM64": exit status 1
```

It also causes an unexpected structure in the "dist" output, which is not typically used for anything, but might still
cause confusion during unrelated development or troubleshooting.

Author: per1234

DistTasks.yml

@@ -210,7 +210,7 @@ tasks:
         sha256sum {{.PACKAGE_NAME}} >> {{.CHECKSUM_FILE}}
 
     vars:
-      PLATFORM_DIR: "{{.PROJECT_NAME}}_linux_arm_6"
+      PLATFORM_DIR: "{{.PROJECT_NAME}}_linux_arm_64"
       BUILD_COMMAND: "go build -o {{.DIST_DIR}}/{{.PLATFORM_DIR}}/{{.PROJECT_NAME}} {{.LDFLAGS}}"
       BUILD_PLATFORM: "linux/arm64"
       CONTAINER_TAG: "{{.GO_VERSION}}-arm"