Bump composer/composer from 1.4.2 to 1.7.3

Bumps [composer/composer](https://github.com/composer/composer) from 1.4.2 to 1.7.3.
- [Release notes](https://github.com/composer/composer/releases)
- [Changelog](https://github.com/composer/composer/blob/master/CHANGELOG.md)
- [Commits](composer/composer@1.4.2...1.7.3)

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

Author: dependabot-support