[CMake] Fix pkg-config name of JPEGXL

https://bugs.webkit.org/show_bug.cgi?id=259198

Reviewed by Carlos Alberto Lopez Perez and Adrian Perez de Castro.

This is the correct pkg-config name:

https://github.com/libjxl/libjxl/blob/main/lib/jxl/libjxl.pc.in

* Source/cmake/FindJPEGXL.cmake:

Canonical link: https://commits.webkit.org/266046@main

Source/cmake/FindJPEGXL.cmake

@@ -54,7 +54,7 @@ This will define the following variables in your project:
 
 find_package(PkgConfig QUIET)
 if (PkgConfig_FOUND)
-    pkg_check_modules(PC_JPEGXL QUIET jxl)
+    pkg_check_modules(PC_JPEGXL QUIET libjxl)
     set(JPEGXL_COMPILE_OPTIONS ${PC_JPEGXL_CFLAGS_OTHER})
     set(JPEGXL_VERSION ${PC_JPEGXL_VERSION})
 endif ()