Fix typo in test name

[dsanders11]

Issue #, if available:

Description of changes:

Test name had a typo, CaseInsensiveDict. Changed to TestCaseInsensitiveDict to avoid name collision with the correctly spelled CaseInsensitiveDict.

Checklist:

• Write Design Document (Do I need to write a design document?)
• Write unit tests
• Write/update functional tests
• Write/update integration tests
• make pr passes
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[dsanders11]

Build failure seems unrelated.

[jfuss]

This was removed in #1166 to use Headers object instead. Therefore this is patch is no longer needed. Closing