ci: Use actions/checkout@v2.

There's a race condition with v1 that we seem to be encountering.

Author: dewyatt

.github/workflows/centos7.yml

@@ -37,7 +37,7 @@ jobs:
             RNP_TESTS: rnp_tests
     env: ${{ matrix.env }}
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: Add rnpuser
         run: |
           useradd rnpuser

.github/workflows/coverity.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: Setup environment
         run: |
           . ci/gha/setup-env.inc.sh

.github/workflows/lint.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     if: "!contains(github.event.head_commit.message, 'skip ci')"
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - uses: DoozyX/clang-format-lint-action@v0.5
         with:
           clangFormatVersion: 9

.github/workflows/macos.yml

@@ -18,7 +18,7 @@ jobs:
     if: "!contains(github.event.head_commit.message, 'skip ci')"
     timeout-minutes: 50
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: Setup environment
         run: |
           . ci/gha/setup-env.inc.sh

.github/workflows/ubuntu.yml

@@ -18,7 +18,7 @@ jobs:
     if: "!contains(github.event.head_commit.message, 'skip ci')"
     timeout-minutes: 50
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: Setup environment
         run: |
           . ci/gha/setup-env.inc.sh

.github/workflows/windows.yml

@@ -20,7 +20,7 @@ jobs:
     steps:
       - name: Disable git eol translation
         run: git config --global core.autocrlf false
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: Add MSYS2 path
         uses: MSP-Greg/msys2-action/add_paths@master
       - name: Update MSYS2