fix: Upgrade fast-xml-parser to fix RangeError DoS (#11598)
## Summary
Fixes a high severity RangeError DoS vulnerability in fast-xml-parser.
- **Package**: fast-xml-parser
- **Vulnerable versions**: >=4.3.6 <=5.3.3
- **Fixed version**: 5.3.4
- **Severity**: High
- **Dependency path**: docs/site > fumadocs-openapi > openapi-sampler >
fast-xml-parser
Since `openapi-sampler` specifies `fast-xml-parser@^4.5.0` as a
dependency, we cannot resolve this by upgrading fumadocs-openapi. This
PR adds a pnpm override in the root package.json to force
`fast-xml-parser>=5.3.4`.
Closes TURBO-5148
