Bump actions/checkout from 2 to 2.3.4 (#338)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 2.3.4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v2.3.4)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/freebsd.yml

@@ -16,7 +16,7 @@ jobs:
     # See https://github.com/vmactions/freebsd-vm#under-the-hood.
     runs-on: macos-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v2.3.4
     - name: Test
       id: build-freebsd
       uses: vmactions/[email protected]

.github/workflows/haskell-ci.yml

@@ -139,7 +139,7 @@ jobs:
           if [ $((HCNUMVER >= 80000 && HCNUMVER < 90000)) -ne 0 ] ; then $CABAL --store-dir=$HOME/.haskell-ci-tools/store v2-install $ARG_COMPILER --ignore-project -j2 doctest --constraint='doctest ^>=0.17' ; fi
           if [ $((HCNUMVER >= 80000 && HCNUMVER < 90000)) -ne 0 ] ; then doctest --version ; fi
       - name: checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v2.3.4
         with:
           path: source
       - name: initial cabal.project for sdist

.github/workflows/windows_and_macOS.yml

@@ -18,7 +18,7 @@ jobs:
         ghc: ['9.0']
       fail-fast: false
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v2.3.4
     - uses: haskell/actions/[email protected]
       id: setup-haskell-cabal
       with: