[BUGFIX] Prepare changed json_response middleware

The json_response functional test extension will soon
avoid returning json encoded responses. This will make
the functional frontend test suite fully transparent
regarding responses.
This patch prepares a couple of frontend functional
tests towards this change.

Resolves: #96112
Releases: master, 11.5
Change-Id: I8116caf08e4b8b76ad5d23b49954d9cb78d1c4de
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72319


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/frontend/Tests/Functional/SiteHandling/SlugSiteRequestTest.php

@@ -865,14 +865,13 @@ class SlugSiteRequestTest extends AbstractTestCase
             $this->internalRequestContext
                 ->withFrontendUserId($frontendUserId)
         );
-        $json = json_decode((string)$response->getBody(), true);
 
         self::assertSame(
             403,
             $response->getStatusCode()
         );
         self::assertThat(
-            $json['body'] ?? null,
+            (string)$response->getBody(),
             self::logicalOr(
                 self::stringContains('That page is forbidden to you'),
                 self::stringContains('ID was not an accessible page'),
@@ -1029,14 +1028,13 @@ class SlugSiteRequestTest extends AbstractTestCase
             $this->internalRequestContext
                 ->withFrontendUserId($frontendUserId)
         );
-        $json = json_decode((string)$response->getBody(), true);
 
         self::assertSame(
             403,
             $response->getStatusCode()
         );
         self::assertThat(
-            $json['body'] ?? null,
+            (string)$response->getBody(),
             self::logicalOr(
                 self::stringContains('That page is forbidden to you'),
                 self::stringContains('ID was not an accessible page'),
@@ -1226,13 +1224,13 @@ class SlugSiteRequestTest extends AbstractTestCase
             new InternalRequest($uri),
             $this->internalRequestContext
         );
-        $json = json_decode((string)$response->getBody(), true);
+
         self::assertSame(
             404,
             $response->getStatusCode()
         );
         self::assertThat(
-            $json['body'] ?? null,
+            (string)$response->getBody(),
             self::stringContains('That page was not found')
         );
     }