Fixes #18075: fixed Dockerfile warning

[kuma0128]

Describe your changes:

This is my first PR to OSS.
Fixes #18075

I have fixed the warnings mentioned below.

2 warnings found (use docker --debug to expand):

• LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format
• FromAsCasing: 'as' and 'FROM' keywords' casing do not match
  

Type of change:

• Bug fix
• Improvement
• New feature
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation

Checklist:

• I have read the CONTRIBUTING document.
• My PR title is Fixes <issue-number>: <short explanation>
• I have commented on my code, particularly in hard-to-understand areas.
• For JSON Schema changes: I updated the migration scripts or explained why it is not needed.

[github-actions]

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