Update infection/infection requirement from ^0.15.3 to ^0.16.6

Created by: dependabot[bot]

Updates the requirements on infection/infection to permit the latest version.

Release notes

Sourced from infection/infection's releases.

Update GPG private key as the old one expired

Changed:

• Update GPG private key as the old one expired

Commits

• d43267a Update GPG private key as the old one expired
• f02709e Restrict installing with faulty versions of PHPUnit's coverage package (#1295)
• c1ef0b1 Respect list of source directories (#1277)
• 52d597a Install test framework adapters as dev dependencies (#1262)
• 9a3bca9 Return back $finder->notPath($excludedDir) to filter out excluded files con...
• 1928f71 Cast Mutator's setting objectto array before using (#1230)
• b02a5a2 Fix Travis CI builds (#1201)
• c538af7 Benchmark for JUnitTestCaseSorter::uniqueByTestFile (#1177)
• d38b6cb Update CHANGELOG.md for with 0.16.0 changes
• e44e782 Сheck adapter from infection.json config file in order to install a package (...
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