installation-test - drop Python 3.7

Seems updated aiohttp is not available for it anymore,
drop it from the matrix. Python 3.7 is anyways end-of-life,
so you should not use it anymore.

We get error when trying on Ubuntu 20.04.
```
 ERROR: No matching distribution found for aiohttp==3.9.0
```

Ref:
- https://endoflife.date/python

.github/workflows/installation-test.yml

@@ -17,7 +17,7 @@ jobs:
     strategy:
         matrix:
             os: ["ubuntu-20.04", "ubuntu-22.04"]
-            python-ver: ["3.7", "3.8", "3.9", "3.10", "3.11"]
+            python-ver: ["3.8", "3.9", "3.10", "3.11"]
             exclude:
                 - os: ubuntu-22.04
                   python-ver: 3.6