Bump actions/checkout from 2 to 2.3.4 (#425)

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/cd.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v2.3.4
 
       - name: Install Rust
         uses: actions-rs/toolchain@v1

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
         rust: [stable, nightly]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v2.3.4
 
     - name: Restore cargo cache
       uses: actions/[email protected]
@@ -48,7 +48,7 @@ jobs:
     name: Rustfmt
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v2.3.4
     - name: Install Rust
       uses: actions-rs/toolchain@v1
       with:
@@ -60,7 +60,7 @@ jobs:
     name: Security audit
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v2.3.4
     - uses: actions-rs/audit-check@v1
       with:
         token: ${{ secrets.GITHUB_TOKEN }}