chore: Prevent node 20 from running on AL2, fix transcribe expectation

[jbelkins]

Issue #

#1608

Description of changes

• Disable the forcing of Github Actions onto Node 20 since AL2 is incompatible with that version of Node.
• The Transcribe Streaming integration test transcription has been changed slightly by the service. Verification of the transcription is now case-insensitive, and allows for any of the previous variations that the service has returned.

New/existing dependencies impact assessment, if applicable

No new dependencies were added to this change.

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