Packages - force python 3.9 (#5206)

* specify python 3.9

* now support 12 too

* rmove 12

* change deps

* add dedicated wheel install

* add dev headers (for rappidfuzz)

.pkgr.yml

@@ -19,8 +19,9 @@ before:
   - contrib/packager.io/before.sh
 dependencies:
   - curl
-  - python3
-  - python3-venv
+  - python3.9
+  - python3.9-venv
+  - python3.9-dev
   - python3-pip
   - python3-cffi
   - python3-brotli