fix: handle double charset everywhere by using our ParseMediaType

internal/users/mocks/mocks.go

@@ -5,11 +5,12 @@
 package mocks
 
 import (
+	reflect "reflect"
+
 	store "github.com/ProtonMail/proton-bridge/internal/store"
 	credentials "github.com/ProtonMail/proton-bridge/internal/users/credentials"
 	pmapi "github.com/ProtonMail/proton-bridge/pkg/pmapi"
 	gomock "github.com/golang/mock/gomock"
-	reflect "reflect"
 )
 
 // MockConfiger is a mock of Configer interface