ci: Drop python-3.7, add python-3.12

Even though python-3.7 remains our minimal Python version it is not
support by GH actions anymore so this commit drops it from CI. We also
add a setup for the now released python-3.12.

.github/workflows/btest.yml

@@ -12,7 +12,7 @@ jobs:
   Run-BTest:
     strategy:
       matrix:
-        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
         os: [macos-latest, ubuntu-latest, windows-latest]
 
     runs-on: ${{ matrix.os }}
@@ -53,7 +53,7 @@ jobs:
   Test-SetupPY:
     strategy:
       matrix:
-        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
         os: [ubuntu-latest]
 
     runs-on: ${{ matrix.os }}