install-qt-action v2.12.0

• Setting environment variables is now optional
• Set LD_LIBRARY_PATH on linux
• Set IQTA_TOOLS env variable for finding tools slightly more easily
• Update py7zr default version to 0.11.3
• Update aqtinstall default version to 0.11.1 (This should fix aqtinstall not working when qt's download mirror is down, like it is right now)
• Removed mirror input option because its a little pointless now (you can still use it with the extra input)