[ci] Update to actions/checkout@v3 to silence GitHub warnings

Signed-off-by: Michael Brown <mcb30@ipxe.org>

.github/workflows/build.yml

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 6dc577e..f8ba4e1 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -9,7 +9,7 @@
     runs-on: ubuntu-20.04
     steps:
       - name: Check out code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           fetch-depth: 0
       - name: Install packages
@@ -35,7 +35,7 @@
     runs-on: ubuntu-20.04
     steps:
       - name: Check out code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           fetch-depth: 0
       - name: Install packages
@@ -55,7 +55,7 @@
     runs-on: ubuntu-20.04
     steps:
       - name: Check out code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           fetch-depth: 0
       - name: Install packages

.github/workflows/coverity.yml

diff --git a/.github/workflows/coverity.yml b/.github/workflows/coverity.yml
index 20634be..d27eae1 100644
--- a/.github/workflows/coverity.yml
+++ b/.github/workflows/coverity.yml
@@ -11,7 +11,7 @@
     runs-on: ubuntu-20.04
     steps:
       - name: Check out code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Download Coverity Scan
         run: |
           curl --form token=${{ secrets.COVERITY_SCAN_TOKEN }} \