GitHub Actions: Use new PHP workflows

[sukhwinder33445]

This PR switches to the new PHP workflow, which combines linting, static analysis, and unit testing. phpcs.xml and phpunit.xml have been removed, as the new workflow provides sane defaults for both and the files did not contain any special configurations anyway. Since the new workflow uses the latest PHPUnit version by default, deprecated PHPUnit features have been migrated. In addition, code style corrections were made to comply with the latest PSR coding standards. PHPStan scanDirectories was adjusted so that tests are always run with the dependencies installed by composer install.

• After merging, @lippserd will update the branch protection required status checks to match the new workflow - below is a dry run showing what would happen.

./gh-update-branch-protection-checks/gh-update-branch-protection-checks.sh --repo Icinga/ipl-html --pr 185 --dry-run
[INFO] Fetching PR details...
[WARNING] PR #185 is not merged; continuing anyway...
[INFO] Target branch: main
[INFO] PR head branch: php-workflows
[INFO] PR head commit SHA: 1e030f76148178011c30aa16152671498e76a945
[INFO] Listing workflow runs triggered by commit 1e030f76148178011c30aa16152671498e76a945...
[INFO] Workflow runs: 20131545127
[INFO] Listing jobs for workflow 20131545127...
[INFO] Jobs: PHP / Static analysis (8.4) / PHPStan 8.4, PHP / Lint (8.2) / Linters 8.2, PHP / Static analysis (8.2) / PHPStan 8.2, PHP / Lint (8.4) / Linters 8.4, PHP / Lint (8.3) / Linters 8.3, PHP / Test (8.4) / PHPUnit 8.4, PHP / Test (8.3) / PHPUnit 8.3, PHP / Lint (8.5) / Linters 8.5, PHP / Static analysis (8.5) / PHPStan 8.5, PHP / Static analysis (8.3) / PHPStan 8.3, PHP / Test (8.2) / PHPUnit 8.2, PHP / Test (8.5) / PHPUnit 8.5
[INFO] Fetching current branch protection required status checks...
[INFO] Comparing branch protection required status checks...
--- /dev/fd/63	2025-12-11 13:09:19.205593449 +0100
+++ /dev/fd/62	2025-12-11 13:09:19.205942658 +0100
@@ -43,27 +43,51 @@
       },
       {
         "app_id": 15368,
-        "context": "Static analysis for php 8.2 on ubuntu-latest"
+        "context": "PHP / Lint (8.2) / Linters 8.2"
       },
       {
         "app_id": 15368,
-        "context": "Static analysis for php 8.3 on ubuntu-latest"
+        "context": "PHP / Lint (8.3) / Linters 8.3"
       },
       {
         "app_id": 15368,
-        "context": "Static analysis for php 8.4 on ubuntu-latest"
+        "context": "PHP / Lint (8.4) / Linters 8.4"
       },
       {
         "app_id": 15368,
-        "context": "Unit tests with php 8.2 on ubuntu-latest"
+        "context": "PHP / Lint (8.5) / Linters 8.5"
       },
       {
         "app_id": 15368,
-        "context": "Unit tests with php 8.3 on ubuntu-latest"
+        "context": "PHP / Static analysis (8.2) / PHPStan 8.2"
       },
       {
         "app_id": 15368,
-        "context": "Unit tests with php 8.4 on ubuntu-latest"
+        "context": "PHP / Static analysis (8.3) / PHPStan 8.3"
+      },
+      {
+        "app_id": 15368,
+        "context": "PHP / Static analysis (8.4) / PHPStan 8.4"
+      },
+      {
+        "app_id": 15368,
+        "context": "PHP / Static analysis (8.5) / PHPStan 8.5"
+      },
+      {
+        "app_id": 15368,
+        "context": "PHP / Test (8.2) / PHPUnit 8.2"
+      },
+      {
+        "app_id": 15368,
+        "context": "PHP / Test (8.3) / PHPUnit 8.3"
+      },
+      {
+        "app_id": 15368,
+        "context": "PHP / Test (8.4) / PHPUnit 8.4"
+      },
+      {
+        "app_id": 15368,
+        "context": "PHP / Test (8.5) / PHPUnit 8.5"
       }
     ],
     "contexts_url": "https://api.github.com/repos/Icinga/ipl-html/branches/main/protection/required_status_checks/contexts",
[SUCCESS] [dry-run] No changes applied.

[lippserd]

I have updated the branch protection required status checks to match the new workflow.