Update sirbrillig/phpcs-variable-analysis requirement (#247)

Updates the requirements on [sirbrillig/phpcs-variable-analysis](https://github.com/sirbrillig/phpcs-variable-analysis) to permit the latest version.
- [Release notes](https://github.com/sirbrillig/phpcs-variable-analysis/releases)
- [Commits](sirbrillig/phpcs-variable-analysis@v2.11.17...v2.11.18)

---
updated-dependencies:
- dependency-name: sirbrillig/phpcs-variable-analysis
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

composer.json

@@ -14,7 +14,7 @@
   "require": {
     "php": "^7.2 || ^8.0",
     "phpcompatibility/phpcompatibility-wp": "2.1.4",
-    "sirbrillig/phpcs-variable-analysis": "2.11.17",
+    "sirbrillig/phpcs-variable-analysis": "2.11.18",
     "slevomat/coding-standard": "8.14.1",
     "wp-coding-standards/wpcs": "3.0.1"
   },