Use latest action versions in example workflow snippets

The documentation includes some snippets of GitHub Actions workflows. In addition to arduino/report-size-deltas, these
workflows use some additional actions.

Although not essential for the purposes of documenting the usage of this project, it will be better to use the latest
version of these action dependencies to make it more likely that the readers will do the same in their own real
workflows.

Author: per1234

README.md

@@ -83,11 +83,11 @@ jobs:
   compile:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: arduino/compile-sketches@v1
         with:
           enable-deltas-report: true
-      - uses: actions/upload-artifact@v2
+      - uses: actions/upload-artifact@v3
         with:
           name: sketches-reports
           path: sketches-reports
@@ -110,7 +110,7 @@ jobs:
           - "arduino:avr:uno"
           - "arduino:samd:mkrzero"
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - uses: arduino/compile-sketches@v1
         with:
@@ -120,7 +120,7 @@ jobs:
 
       # This step is needed to pass the size data to the report job 
       - name: Upload sketches report to workflow artifact
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v3
         with:
           name: ${{ env.SKETCHES_REPORTS_ARTIFACT_NAME }}
           path: ${{ env.SKETCHES_REPORTS_PATH }}
@@ -133,7 +133,7 @@ jobs:
     steps:
       # This step is needed to get the size data produced by the compile jobs
       - name: Download sketches reports artifact
-        uses: actions/download-artifact@v2
+        uses: actions/download-artifact@v3
         with:
           name: ${{ env.SKETCHES_REPORTS_ARTIFACT_NAME }}
           path: ${{ env.SKETCHES_REPORTS_PATH }}