`long_description` has syntax errors in markup and would not be rendered on PyPI when 'npm run package'

## :bug: Bug Report

### Affected Languages
- [ ] `TypeScript` or `Javascript`
- [x] `Python`
- [ ] `Java`
- [ ] .NET (`C#`, `F#`, ...)

### General Information
* **JSII Version:** 6.13.6
* **Platform:** 4.19.84-microsoft-standard #1 SMP Wed Nov 13 11:44:37 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

### What is the problem?
When attempting to Package a JSII module I get the following error:

```
> jsii-pacmak

Error: Process exited with status 1
Checking /mnt/c/Users/xxxx/secure-bucket/dist/python/mbonig.secure_bucket-1.0.0-py3-none-any.whl: FAILED `long_description` has syntax errors in markup and would not be rendered on PyPI.
line 11: Warning: Inline literal start-string without end-string.
warning: `long_description_content_type` missing. defaulting to `text/x-rst`.
```

### Verbose Log

```
> jsii-pacmak "--verbose"

[jsii-pacmak] [INFO] Found 1 modules to package
[jsii-pacmak] [INFO] Packaging NPM bundles
[jsii-pacmak] [INFO] Loading jsii assemblies and translations
[jsii-pacmak] [INFO] Packaging 'python' for secure-bucket
[jsii-pacmak] [INFO] Packaging 'java' for secure-bucket
[jsii-pacmak] [INFO] Packaging 'dotnet' for secure-bucket
[jsii-pacmak] [INFO] Packaging 'js' for secure-bucket
[jsii-pacmak] [INFO] js finished
Error: Process exited with status 1
Checking /mnt/c/Users/xxx/secure-bucket/dist/python/mbonig.secure_bucket-1.0.0-py3-none-any.whl: FAILED `long_description` has syntax errors in markup and would not be rendered on PyPI.
line 11: Warning: Inline literal start-string without end-string.
warning: `long_description_content_type` missing. defaulting to `text/x-rst`.
Checking /mnt/c/Users/mboni/projects/secure-bucket/dist/python/mbonig.secure-bucket-1.0.0.tar.gz: PASSED

at ChildProcess. (/mnt/c/Users/mboni/projects/secure-bucket/node_modules/jsii-pacmak/lib/util.js:57:31) at Object.onceWrapper (events.js:300:26)
at ChildProcess.emit (events.js:210:5)
at maybeClose (internal/child_process.js:1021:16)
at Process.ChildProcess._handle.onexit (internal/child_process.js:283:5)
```

Reproduce the failure with `npm run package` and inspect the generated `dist/python` wheel and the `jsii-pacmak` packaging path referenced in `node_modules/jsii-pacmak/lib/util.js`. Check how `long_description` and `long_description_content_type` are produced; done means the Python package validation passes without markup syntax errors or the missing-content-type warning.

Written by the indexing model from the issue text.