GitHub: Add problem matcher for file header checker.
diff --git a/.github/fileheader.json b/.github/fileheader.json
new file mode 100644
index 0000000..cb0492b
--- /dev/null
+++ b/.github/fileheader.json
@@ -0,0 +1,16 @@
+{
+	"problemMatcher": [
+		{
+			"owner": "fileheader",
+			"severity": "error",
+			"pattern": [
+				{
+					"regexp": "^(.*):(\\d+):(.*)$",
+					"file": 1,
+					"line": 2,
+					"message": 3
+				}
+			]
+		}
+	]
+}
diff --git a/.github/workflows/fileheader.yml b/.github/workflows/fileheader.yml
index 8e453cf..37f213d 100644
--- a/.github/workflows/fileheader.yml
+++ b/.github/workflows/fileheader.yml
@@ -25,6 +25,7 @@
       uses: jitterbit/get-changed-files@v1
     - name: Check changed files
       run: |
+        echo "::add-matcher::.github/fileheader.json"
         RC=0
         for changed_file in ${{ steps.files.outputs.all }}; do
           ./CMSIS/Utilities/check_header.sh ${changed_file} || RC=1