github: update actions/checkout to v3

This fixes deprecation warnings about node v12.

.github/workflows/build.yml

@@ -26,7 +26,7 @@ jobs:
         python-version: [3.8, 3.9]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         submodules: recursive
     - name: Set up Python ${{ matrix.python-version }}

.github/workflows/publish-ide-docs.yml

@@ -13,7 +13,7 @@ jobs:
       run: |
         sudo apt-get update
         sudo apt-get install -y dvisvgm preview-latex-style texlive texlive-fonts-extra texlive-latex-extra
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         submodules: recursive
     - name: Set up Python 3.8

.github/workflows/publish-jedi.yml

@@ -9,7 +9,7 @@ jobs:
   publish_jedi:
     runs-on: ubuntu-22.04
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     # Setup .npmrc file to publish to npm
     - uses: actions/setup-node@v3
       with: