fix: remove redundant string cast on getHeaderLine return value

getHeaderLine() already returns string per PSR-7; Psalm flags the
(string) cast as RedundantCast.

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

src/NextcloudApiContext.php

@@ -361,7 +361,7 @@ public function theResponseShouldHaveStatusCode(string $code): void {
 
 	#[Given('the response header :header should contain :value')]
 	public function theResponseHeaderShouldContain(string $header, string $value): void {
-		$actual = strtolower((string)$this->response->getHeaderLine($header));
+		$actual = strtolower($this->response->getHeaderLine($header));
 		Assert::assertStringContainsString(strtolower($value), $actual, sprintf('Response header "%s" does not contain "%s"', $header, $value));
 	}