[SYCL][Matrix] Amend CODEOWNERS for check_device_code matrix tests (intel#14088)

CODEOWNERS seems to be missing a line attributing
`sycl/test/check_device_code/matrix` tests to
intel/sycl-matrix-reviewers (As per [this
discussion](intel#14063 (comment))).
This PR remedies this.

Although, I noticed the current CODEOWNERS section for the matrix
reviewers uses paths; Let me know if I should use `sycl/**/matrix`
instead.

Author: ianayl

.github/CODEOWNERS

@@ -126,6 +126,7 @@ sycl/test-e2e/KernelFusion @intel/dpcpp-kernel-fusion-reviewers
 sycl/include/sycl/ext/oneapi/matrix/ @intel/sycl-matrix-reviewers
 sycl/test-e2e/Matrix @intel/sycl-matrix-reviewers
 sycl/test/matrix @intel/sycl-matrix-reviewers
+sycl/test/check_device_code/matrix @intel/sycl-matrix-reviewers
 
 # Native CPU
 llvm/**/*SYCLNativeCPU* @intel/dpcpp-nativecpu-pi-reviewers