CI: upgrade all Github Actions.

Author: jfng

.github/workflows/main.yml

@@ -31,11 +31,11 @@ jobs:
     name: 'test (${{ matrix.python-version }}, HDL ${{ matrix.amaranth-version }})'
     steps:
       - name: Check out source code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Set up PDM
-        uses: pdm-project/setup-pdm@v3
+        uses: pdm-project/setup-pdm@v4
         with:
           python-version: ${{ matrix.python-version }}
       - name: Install dependencies
@@ -61,14 +61,14 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out source code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Fetch tags from upstream repository
         run: |
           git fetch --tags https://github.com/amaranth-lang/amaranth-stdio.git
       - name: Set up PDM
-        uses: pdm-project/setup-pdm@v3
+        uses: pdm-project/setup-pdm@v4
         with:
           python-version: '3.12'
       - name: Install dependencies
@@ -78,7 +78,7 @@ jobs:
         run: |
           pdm run document
       - name: Upload documentation archive
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: docs
           path: docs/_build
@@ -98,11 +98,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out source code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Download documentation archive
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: docs
           path: docs/
@@ -131,11 +131,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out source code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Download documentation archive
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: docs
           path: pages/docs/${{ github.ref_name }}/