Sheets `clear` operation breaks with HTTP/2

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### A screenshot that you have tested with "Try this API".

N/A

### Link to the code that reproduces this issue. A link to a **public** Github Repository or gist with a minimal reproduction.

https://gist.github.com/neil-lobo/e632aae751fe7aec8bbc29a42c585015

### A step-by-step description of how to reproduce the issue, based on the linked reproduction.

1. Save `credentials.json` file with correct access to sheet to root of project
2. Replace `[sheet ID]` with accessible sheet
3. Run script
4. Observe output
5. Turn off http2
6. Observe output
### A clear and concise description of what the bug is, and what you expected to happen.

Using the http2 option, the clear operation does not work. I assume https://github.com/googleapis/google-api-nodejs-client/issues/1801#issuecomment-524921412 is no longer the case since there is an explicit option to enable http2 now.

Referring to the gist, the expected output is
```
finish get 200
finish clear 200

```

however the output is
```
finish get 200

```

Disabling http2 produces the correct output. Note that this is not simply a response issue, the operation itself does not reflect in the specified sheet.

### A clear and concise description WHY you expect this behavior, i.e., was it a recent change, there is documentation that points to this behavior, etc. **

Breaks usage

Start with the linked public gist and reproduce the Sheets clear operation with HTTP/2 enabled, then compare it with the working HTTP/1.1 behavior. Trace the client path used by the gist and verify the fix by observing a successful clear response and the specified sheet actually being cleared.

索引モデルが issue の本文から書いたものです。