[Az Resources] Fix resource tags casing serialization - tags casing not being preserved when passed as parameters

[jorgecotillo]

Description

We've encountered that after this PR got merged: #15552 we regressed the way casing is handled on the template parameters. Basically casing was not preserved and it affected the way resource tags works.

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
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  • For any service, the ChangeLog.md file can be found at src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md
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• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
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[shenglol]

The unit test Microsoft.Azure.Commands.Resources.Test.Json.PSJsonSerializerTests.Serialize_Hashtable_Success failed, otherwise it looks good to me.

[jorgecotillo]

The unit test Microsoft.Azure.Commands.Resources.Test.Json.PSJsonSerializerTests.Serialize_Hashtable_Success failed, otherwise it looks good to me.

Thanks Shenglong, yeah Gokul mentioned it to me as well, I just fixed the test.

[Xynoclafe]

lgtm