⬆️ Drop support for Python 3.7, require Python 3.8 or above (#10442)

* 📝 Update docs, require Python 3.8+, drop 3.7

* 🔧 Update pyproject.toml, drop support for Python 3.7, require Python 3.8+

* 👷 Update CI GitHub Actions, drop support for Python 3.7, require 3.8+

* 📝 Update docs' references to Python 3.6 and 3.7, use Python 3.8

docs/uk/docs/tutorial/encoder.md

@@ -26,7 +26,7 @@
     {!> ../../../docs_src/encoder/tutorial001_py310.py!}
     ```
 
-=== "Python 3.6+"
+=== "Python 3.8+"
 
     ```Python hl_lines="5  22"
     {!> ../../../docs_src/encoder/tutorial001.py!}