Fixes dropdown breaking if a user types in invalid value and presses enter

[abidlabs]

Fixes: #5540

Repro:

import gradio as gr

with gr.Blocks() as demo:
    with gr.Row():
        with gr.Column():
            dropdown = gr.Dropdown(
                choices=["abc", "def", "ghi"],
                value="abc",
                allow_custom_value=False,
            )
            button = gr.Button()
        with gr.Column():
            out = gr.Textbox()

    button.click(fn=lambda x: x, inputs=dropdown, outputs=out)

if __name__ == "__main__":
    demo.queue().launch()

Notably, the Multiselect was not experiencing this bug.

Adds a couple of unit tests which don't actually test this exact bug (I couldn't figure out simulating the enter key -- tried keyboard("{Enter}") but it wasn't working for me), but they do test related behavior.

[gradio-pr-bot]

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---

Install Gradio from this PR

pip install https://gradio-builds.s3.amazonaws.com/bcb0df4630fdb5056212a774dac77f953c36617c/gradio-3.44.1-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@bcb0df4630fdb5056212a774dac77f953c36617c#subdirectory=client/python"

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/dropdown	patch
gradio	patch

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With the following changelog entry.

Fixes dropdown breaking if a user types in invalid value and presses enter

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[hysts]

Thanks for the quick fix! I tested it and it works fine for me.