PHPUnit tweaks

[jrfnl]

PHPUnit: update configuration

PHPUnit recently released version 9.5.10 (and 8.5.21).

This contains a particular (IMO breaking) change:

• PHPUnit no longer converts PHP deprecations to exceptions by default (configure convertDeprecationsToExceptions="true" to enable this)

Let's unpack this:

Previously (PHPUnit < 9.5.10/8.5.21), if PHPUnit would encounter a PHP native deprecation notice, it would:

1. Show a test which causes a deprecation notice to be thrown as "errored",
2. Show the first deprecation notice it encountered and
3. PHPUnit would exit with a non-0 exit code (2), which will fail a CI build.

As of PHPUnit 9.5.10/8.5.21, if PHPUnit encounters a PHP native deprecation notice, it will no longer do so. Instead PHPUnit will:

1. Show a test which causes a PHP deprecation notice to be thrown as "risky",
2. Show the all deprecation notices it encountered and
3. PHPUnit will exit with a 0 exit code, which will show a CI build as passing.

This commit reverts PHPUnit to the previous behaviour by adding convertDeprecationsToExceptions="true" to the PHPUnit configuration.
It also adds the other related directives for consistency.

Refs:

• https://github.com/sebastianbergmann/phpunit/blob/9.5/ChangeLog-8.5.md
• https://github.com/sebastianbergmann/phpunit/blob/9.5/ChangeLog-9.5.md

.gitignore: add PHPUnit cache file

Since PHPUnit 8.x, PHPUnit generates a cache file. This file should not be committed.

[jrfnl]

Rebased after merge of #35