CI: Use CrateDB nightly for PRs on Linux, lock version only on macOS

Problem: There are no nightly builds for macOS, so the test matrix has
an anomaly. C'est la vie.

Author: amotl

.github/workflows/tests.yml

@@ -16,23 +16,23 @@ jobs:
      on ${{ matrix.os }}"
     runs-on: ${{ matrix.os }}
     strategy:
+      fail-fast: false
       matrix:
-        os: ['ubuntu-22.04', 'macos-latest']
+        os: ['ubuntu-22.04']
         python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12', '3.13']
-        cratedb-version: ['5.8.3']
+        cratedb-version: ['nightly']
 
         # To save resources, only verify the most recent Python versions on macOS.
-        exclude:
-          - os: 'macos-latest'
-            python-version: '3.7'
+        include:
           - os: 'macos-latest'
-            python-version: '3.8'
+            cratedb-version: '5.9.2'
+            python-version: '3.11'
           - os: 'macos-latest'
-            python-version: '3.9'
+            cratedb-version: '5.9.2'
+            python-version: '3.12'
           - os: 'macos-latest'
-            python-version: '3.10'
-
-      fail-fast: false
+            cratedb-version: '5.9.2'
+            python-version: '3.13'
 
     env:
       CRATEDB_VERSION: ${{ matrix.cratedb-version }}