Update mantle-framework/testkit requirement from ^0.12 to ^1.1

Updates the requirements on [mantle-framework/testkit](https://github.com/mantle-framework/testkit) to permit the latest version.
- [Commits](mantle-framework/testkit@v0.12.2...v1.1.0)

---
updated-dependencies:
- dependency-name: mantle-framework/testkit
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

composer.json

@@ -24,7 +24,7 @@
     "require-dev": {
         "alleyinteractive/alley-coding-standards": "^2.0",
         "alleyinteractive/wordpress-fieldmanager": "^1.6",
-        "mantle-framework/testkit": "^0.12",
+        "mantle-framework/testkit": "^1.1",
         "szepeviktor/phpstan-wordpress": "^1.3"
     },
     "config": {