more trickle-down CI

.gitattributes

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+/.github        export-ignore
+/phpunit.xml    export-ignore
+/tests          export-ignore

.github/workflows/ci.yml

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+name: CI
+on: [push]
+jobs:
+  build-test:
+    runs-on: ubuntu-latest
+    environment: actions
+    steps:
+      - uses: actions/checkout@master
+      - uses: actions/checkout@v3
+      - uses: php-actions/composer@v6
+      - uses: php-actions/phpunit@v3
+        env:
+          XDEBUG_MODE: coverage
+        with:
+          bootstrap: vendor/autoload.php
+          configuration: phpunit.xml
+          php_extensions: xdebug
+          coverage_clover: coverage.xml
+      - if: success() || failure()
+        uses: codecov/codecov-action@v4
+        with:
+          files: coverage.xml
+          token: ${{ secrets.CODECOV_TOKEN }}

phpunit.xml

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+<?xml version="1.0" encoding="UTF-8" ?>
+<phpunit
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd"
+  executionOrder="depends,defects"
+  requireCoverageMetadata="true"
+  beStrictAboutCoverageMetadata="true"
+  beStrictAboutOutputDuringTests="true"
+>
+  <testsuites>
+    <testsuite name="default">
+      <directory>tests</directory>
+    </testsuite>
+  </testsuites>
+
+  <source
+    restrictDeprecations="true"
+    restrictNotices="true"
+    restrictWarnings="true"
+  >
+    <include>
+      <directory>src</directory>
+    </include>
+  </source>
+</phpunit>