ci: Be explicit about the version of linux and windows runner images

Using the -latest tag is potentially prone to errors, because an update of the tag
could break our CI. This recently happend with macos-latest, which we downgraded
to macos-12 earlier.

Using an explicit version reference makes this problem much less likely - in fact
renovate will pick up new versions once they exist and will suggest updates for it.
Thus, we will see the failures in a related PR instead of randomly everywhere.

.github/workflows/test.yaml

@@ -32,7 +32,7 @@ concurrency:
 jobs:
   coverage:
     name: Coverage
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     defaults:
       run:
         # Hack for enabling color output, see:
@@ -69,7 +69,7 @@ jobs:
       matrix:
         pgVersion: ["9_6", 10, 11, 12, 13, 14, 15, 16]
     name: PG ${{ matrix.pgVersion }}
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     defaults:
       run:
         # Hack for enabling color output, see:
@@ -98,7 +98,7 @@ jobs:
 
   memory:
     name: Memory
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
       - name: Setup Nix Environment
@@ -112,7 +112,7 @@ jobs:
 
   loadtest:
     name: Loadtest
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with: