Downgrade ChatGPT (3.1.5 -> 3.1.4)

The new version is very broken. It has at least 2 issues.

The first one is:

```
Error: maxPromptTokens + max_tokens (3097 + 1024 = 4121) must be less than or equal to maxContextTokens (4097)
    at ChatGPTClient.setOptions (file:///usr/src/app/node_modules/@waylaidwanderer/chatgpt-api/src/ChatGPTClient.js:72:19)
    at new ChatGPTClient (file:///usr/src/app/node_modules/@waylaidwanderer/chatgpt-api/src/ChatGPTClient.js:23:14)
    at main (file:///usr/src/app/dist/index.js:62:21)
    at file:///usr/src/app/dist/index.js:94:1
    at ModuleJob.run (node:internal/modules/esm/module_job:218:25)
    at async ModuleLoader.import (node:internal/modules/esm/loader:329:24)
    at async loadESM (node:internal/process/esm_loader:28:7)
    at async handleMainPromise (node:internal/modules/run_main:113:12)
```

Likely related to:

- https://github.com/matrixgpt/matrix-chatgpt-bot/issues/246
- https://github.com/matrixgpt/matrix-chatgpt-bot/pull/248

It can be tweaked around by overriding some default environment
variables (`roles/custom/matrix-bot-chatgpt/templates/env.j2`) in order to tweak them:

```
CHATGPT_MAX_CONTEXT_TOKENS=4097
CHATGPT_MAX_PROMPT_TOKENS=2500
```

This leads us to another issue:

```
node:internal/process/promises:289
            triggerUncaughtException(err, true /* fromPromise */);
            ^
[Error: Failed to deserialize or serialize a JSON value missing field `version` at line 1 column 6704] {
  code: 'GenericFailure'
}
Node.js v20.11.1
error Command failed with exit code 1.
```

... whatever that means.

roles/custom/matrix-bot-chatgpt/defaults/main.yml

@@ -5,7 +5,7 @@
 matrix_bot_chatgpt_enabled: true
 
 # renovate: datasource=docker depName=ghcr.io/matrixgpt/matrix-chatgpt-bot
-matrix_bot_chatgpt_version: 3.1.5
+matrix_bot_chatgpt_version: 3.1.4
 
 matrix_bot_chatgpt_container_image_self_build: false
 matrix_bot_chatgpt_container_image_self_build_repo: "https://github.com/matrixgpt/matrix-chatgpt-bot"