Update

//If the player is stuck to a wall and is supposed to still be stuck to the wall
if (timeToWallUnstick > 0 && stuckToWall) {

    //If the player hasnt landed yet
    if (!characterController.isGrounded) {

        //Make the player fall at half gravity
        speed.y = verticalVelocity / 2;

        //make sure the player cant leave the wall
        speed -= forbiddenMove;
    }

    /*
    Tick down the time the player has to be "stuck" to the wall
    (counts down from a preset value of 0.25 of a second)
    */
    timeToWallUnstick -= Time.deltaTime;

    /*
    Make sure to have some leway so the player can perform the double jump
    even though they might have left the wall a few fractions of a second
    */
    timeToWalljumpleway -= Time.deltaTime;

} else {
    /*
    If the player isnt supposed to be stuck to the wall anymore, like if
    the timer has run out. make sure to "unstick" from the wall and reset
    the timer back to its original value (0.25 of a second)
    */
    timeToWallUnstick = wallStickTime;
    stuckToWall = false;
}