Raise minimum Python version

This was accidentally lowered in 5d3240d492 and 3.8 has gone EOL since then.

xb.bat

@@ -8,7 +8,7 @@ REM Environment Validation
 REM ============================================================================
 
 SET "PYTHON_MINIMUM_VERSION[0]=3"
-SET "PYTHON_MINIMUM_VERSION[1]=7"
+SET "PYTHON_MINIMUM_VERSION[1]=9"
 CALL :check_python
 IF %_RESULT% NEQ 0 (
   ECHO.

xb.ps1

@@ -14,7 +14,7 @@ foreach ($pythonExecutable in $pythonExecutables) {
     }
 }
 # Neither found, error and exit
-$pythonMinimumVer = 3,7
+$pythonMinimumVer = 3,9
 if (!$pythonPath) {
     Write-FatalError "ERROR: Python $($pythonMinimumVer[0]).$($pythonMinimumVer[1])+ must be installed and on PATH:`nhttps://www.python.org/"
 }

xenia-build

@@ -137,7 +137,7 @@ def main():
         print('')
 
     # Check python version.
-    python_minimum_ver=3,7
+    python_minimum_ver=3,9
     if not sys.version_info[:2] >= (python_minimum_ver[0], python_minimum_ver[1]):
         print('ERROR: Python ', python_minimum_ver[0], '.', python_minimum_ver[1], '+ must be installed and on PATH', sep='')
         sys.exit(1)