[Start] Fix Python 3.11 Unicode Errors

Example Error :
  File "/home/john/freecad-daily-build/Mod/Start/StartPage/StartPage.py", line 422, in handle
    ALTCSS = f.read()
             ^^^^^^^^
  File "/usr/lib/python3.11/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 421: ordinal not in range(128)

src/Mod/Start/StartPage/StartPage.py

@@ -32,6 +32,7 @@ import zipfile
 import re
 import FreeCAD
 import FreeCADGui
+import codecs
 import urllib.parse
 from . import TranslationTexts
 from PySide import QtCore, QtGui
@@ -424,7 +425,7 @@ def handle():
                             "<!--QSS-->", '<style type="text/css">' + ALTCSS + "</style>"
                         )
                 else:
-                    with open(path, "r") as f:
+                    with codecs.open(path, encoding='utf-8') as f:
                         ALTCSS = f.read()
                         HTML = HTML.replace(
                             "<!--QSS-->", '<style type="text/css">' + ALTCSS + "</style>"
@@ -789,9 +790,13 @@ def exportTestFile():
 
     "Allow to check if everything is Ok"
 
-    f = open(os.path.expanduser("~") + os.sep + "freecad-startpage.html", "w")
-    f.write(handle())
-    f.close()
+    with codecs.open(
+        os.path.expanduser("~") + os.sep + "freecad-startpage.html",
+        encoding="utf-8",
+        mode="w",
+    ) as f:
+        f.write(handle())
+        f.close()
 
 
 def postStart(switch_wb=True):