chore: bump rollup-plugin-flat-dts from 1.1.0 to 1.2.0 in /web3.js (#16087)

Bumps [rollup-plugin-flat-dts](https://github.com/run-z/rollup-plugin-flat-dts) from 1.1.0 to 1.2.0.
- [Release notes](https://github.com/run-z/rollup-plugin-flat-dts/releases)
- [Commits](run-z/rollup-plugin-flat-dts@v1.1.0...v1.2.0)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]