Bump actions/checkout from 2 to 3

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v3)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/main.yml

@@ -21,7 +21,7 @@ jobs:
         python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"]
 
     steps:
-      - uses: "actions/checkout@v2"
+      - uses: "actions/checkout@v3"
       - uses: "actions/setup-python@v2"
         with:
           python-version: "${{ matrix.python-version }}"
@@ -61,7 +61,7 @@ jobs:
     runs-on: "ubuntu-latest"
 
     steps:
-      - uses: "actions/checkout@v2"
+      - uses: "actions/checkout@v3"
       - uses: "actions/setup-python@v2"
         with:
           python-version: "3.8"
@@ -87,7 +87,7 @@ jobs:
     runs-on: "${{ matrix.os }}"
 
     steps:
-      - uses: "actions/checkout@v2"
+      - uses: "actions/checkout@v3"
       - uses: "actions/setup-python@v2"
         with:
           python-version: "3.8"