Bumping minimum python support to python 3.9

Pyunifiprotect only supports >=3.9 so, this project must too.

.github/workflows/dev.yml

@@ -20,7 +20,7 @@ jobs:
     # The type of runner that the job will run on
     strategy:
       matrix:
-        python-versions: [3.7, 3.8, 3.9]
+        python-versions: [3.9]
         os: [ubuntu-18.04, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
 

.github/workflows/preview.yml

@@ -18,7 +18,7 @@ jobs:
 
     strategy:
       matrix:
-        python-versions: [ 3.8 ]
+        python-versions: [ 3.9 ]
 
     steps:
       - uses: actions/checkout@v2

.github/workflows/release.yml

@@ -21,7 +21,7 @@ jobs:
 
     strategy:
       matrix:
-        python-versions: [3.8]
+        python-versions: [3.9]
 
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps: