chore: update GitHub Actions to Node.js 24 compatible versions

- actions/checkout: v4 → v6
- actions/upload-artifact: /@v4 (typo) → @v7
- actions/upload-artifact/merge: @v4 → @v7
- actions/download-artifact: @v4 → @v8

Note: arduino/setup-arduino-cli@v2 and AButler/upload-release-assets@v3.0
remain on Node.js 20 — no newer releases available from their maintainers.

Agent-Logs-Url: https://github.com/MRC3742/DIY-Multiprotocol-TX-Module/sessions/1f7fa437-6418-4ff7-9731-3dbc088a6ae0

Co-authored-by: MRC3742 <26642502+MRC3742@users.noreply.github.com>

Author: Copilot

.github/workflows/main.yml

@@ -65,7 +65,7 @@ jobs:
       BOARD: ${{ matrix.board }}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install Arduino CLI
         uses: arduino/setup-arduino-cli@v2
@@ -254,7 +254,7 @@ jobs:
       RELEASE: ${{ matrix.release }}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install Arduino CLI
         uses: arduino/setup-arduino-cli@v2
@@ -338,7 +338,7 @@ jobs:
 
       - name: 'Upload Artifacts'
         if: env.HAVE_FILES == 'true'
-        uses: actions/upload-artifact/@v4
+        uses: actions/upload-artifact@v7
         with:
           name: multi-${{ matrix.release }}
           path: ./binaries/
@@ -349,7 +349,7 @@ jobs:
     needs: [test, build]
     steps:
       - name: Combine and upload build artifacts
-        uses: actions/upload-artifact/merge@v4
+        uses: actions/upload-artifact/merge@v7
         with:
           name: multi-test-build
           pattern: multi-*
@@ -363,7 +363,7 @@ jobs:
     needs: deploy
     steps:
       - name: Download artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: multi-test-build
           path: ./artifacts/