Bump phpunit/phpunit from 9.2.6 to 9.3.7

Sourced from phpunit/phpunit's changelog.

<h2>[9.3.7] - 2020-08-11</h2> <h3>Fixed</h3>

• #4419: --migrate-configuration cannot migrate XML configuration files with multiple <exclude> elements
• #4422: Error when libxml_disable_entity_loader() is used in a data provider

<h2>[9.3.6] - 2020-08-11</h2> <h3>Fixed</h3>

• #4417: Default value for <coverage includeUncoveredFiles="true|false"> XML configuration attribute was false instead of true

<h2>[9.3.5] - 2020-08-10</h2> <h3>Fixed</h3>

• #4412: Code Coverage does not work for isolated test when PHAR is used

<h2>[9.3.4] - 2020-08-10</h2> <h3>Added</h3>

• Added --coverage-cache <directory> CLI option for enabling a cache for static analysis results; it will write its files to <directory>
• Added <coverage cacheDirectory="directory"> XML configuration attribute for enabling a cache for static analysis results; it will write its files to directory
• Added --warm-coverage-cache CLI option for warming the cache for static analysis results; the cache must be configured for this to work

<h3>Fixed</h3>

• #4405: Location for (current version of) XML Schema for XML configuration file has changed
• Default value for <phpunit cacheResult="true|false"> XML configuration attribute was false instead of true

<h2>[9.3.3] - 2020-08-08</h2> <h3>Changed</h3>

• Reverted the workaround for #4399 now that the root cause is fixed in PHP-Scoper

<h3>Fixed</h3>

• #4404: Code Coverage does not work with PHAR and Xdebug
• #4407: PHPUnit 9.3 breaks backward compatibility for assertXmlStringEqualsXmlFile()

<h2>[9.3.2] - 2020-08-07</h2> <h3>Fixed</h3>

• #4402: --no-logging has no effect

<h2>[9.3.1] - 2020-08-07</h2>

• c638a0c Prepare release
• 4cd1764 Update ChangeLog
• b059a35 Leftover from bc5f0c9
• 9ea6f0b Fix issue identified by Psalm
• bc5f0c9 Avoid loading the XML configuration file twice
• 34b048d Update use for new SnapshotNodeList location
• d36811a Use Snapshot list helper to avoid possible incomplete migrations
• bf2f30c Update ChangeLog
• 413a76e Move SnapshotNodeList to Xml namespace
• 232cb85 Fix CS/WS issues
• Additional commits viewable in compare view

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