.github: bump actions to fix Node.js 12 warnings

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

.github/workflows/coverity.yml

@@ -15,8 +15,8 @@ jobs:
   coverity:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/cache@v2
+      - uses: actions/checkout@v3
+      - uses: actions/cache@v3
         id: coverity-toolchain-cache
         with:
           path: cov-analysis-linux64