Alter Fields in multiple feature classes in multiple workspaces

Noob python guy here.

So I have 22 geodatabases all in one folder. Each gdb has two feature classes. For each feature class, I need to rename a few of the fields. I've had success with this code, but it only works for each GDB at a time:

import arcpy
from arcpy import env
env.workspace = r'C:\...\filename.GDB'

for fc in arcpy.ListFeatureClasses('*'):
    try:
        arcpy.AlterField_management(fc, 'ADDR_SN', 'STREET_NAME', 'STREET_NAME')
    except:
        pass

As I said, that code is just for one GDB at a time, so I'd have to change the name in env.workspace each time. That's not a big deal, I just want to see if it's possible to iterate through every GDB in the folder. So I tried adding into the code:

for workspace in arcpy.ListWorkspaces('*', 'All'):

When I add the above code, I also change the env.workspace to the folder name that contains all the geodatabases, but nothing happens. No error is returned, nothing happens. Thanks for your help!