Fix LERDGE 'extends' env references (#21305)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

platformio.ini

 #
 [env:LERDGEX_usb_flash_drive]
 platform          = ${env:LERDGEX.platform}
-extends           = LERDGEX
+extends           = env:LERDGEX
 platform_packages = ${stm32_flash_drive.platform_packages}
 build_flags       = ${stm32_flash_drive.build_flags}
 
 #
 [env:LERDGES_usb_flash_drive]
 platform          = ${env:LERDGES.platform}
-extends           = LERDGES
+extends           = env:LERDGES
 platform_packages = ${stm32_flash_drive.platform_packages}
 build_flags       = ${stm32_flash_drive.build_flags}
 
 #
 [env:LERDGEK_usb_flash_drive]
 platform          = ${env:LERDGEK.platform}
-extends           = LERDGEK
+extends           = env:LERDGEK
 platform_packages = ${stm32_flash_drive.platform_packages}
 build_flags       = ${stm32_flash_drive.build_flags}