fix non-toolchain usage

Author: blink1073

.evergreen/scripts/install-dependencies.sh

@@ -45,6 +45,7 @@ if ! command -v just &>/dev/null; then
     echo "Please install just!"
     exit 1
   fi
+  _BIN_DIR=$PYMONGO_BIN_DIR
   echo "Installing just..."
   mkdir -p "$_BIN_DIR" 2>/dev/null || true
   curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash -s -- $_TARGET --to "$_BIN_DIR" || {
@@ -59,6 +60,7 @@ if ! command -v uv &>/dev/null; then
     echo "Please install uv!"
     exit 1
   fi
+  _BIN_DIR=$PYMONGO_BIN_DIR
   echo "Installing uv..."
   # On most systems we can install directly.
   curl -LsSf https://astral.sh/uv/install.sh | env UV_INSTALL_DIR="$_BIN_DIR" INSTALLER_NO_MODIFY_PATH=1 sh || {