Bump actions/setup-python from 2 to 3

Bumps [actions/setup-python](https://github.com/actions/setup-python) from 2 to 3.
- [Release notes](https://github.com/actions/setup-python/releases)
- [Commits](actions/setup-python@v2...v3)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
       - uses: cisagov/setup-env-github-action@develop
       - uses: actions/checkout@v2
       - id: setup-python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v3
         with:
           python-version: 3.9
       # GO_VERSION and GOCACHE are used by the cache task, so the Go
@@ -118,7 +118,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - id: setup-python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v3
         with:
           python-version: ${{ matrix.python-version }}
       - uses: actions/cache@v2
@@ -163,7 +163,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - id: setup-python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v3
         with:
           python-version: 3.9
       - uses: actions/cache@v2
@@ -205,7 +205,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - id: setup-python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v3
         with:
           python-version: ${{ matrix.python-version }}
       - uses: actions/cache@v2