Accept npm scopes with capital letters in CodeArtifact login

[FiveSlashNine]

Issue #, if available:
#10207

Note:

Npm warns against using uppercase characters in scope names but doesn't block users from doing so. Although newer packages should only have lowercase scope names for several reasons (e.g., case sensitivity across different filesystems), we still want to support older packages and match npm's behavior.

Description of changes:

• Similarly to #10208, this adjusts the regex to accept uppercase characters (A-Z) and adds a conditional that checks case sensitivity and throws a warning.
• Adds three tests for warnings.

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