[CI][Dev] Fix shellcheck errors in the ci/scripts/r_install_system_dependencies.sh #50771

shellcheck r_install_system_dependencies.sh
r_install_system_dependencies.sh: r_install_system_dependencies.sh: openBinaryFile: does not exist (No such file or directory)
palolovalley:arrow hsato$ shellcheck ci/scripts/r_install_system_dependencies.sh

In ci/scripts/r_install_system_dependencies.sh line 22:
: ${ARROW_SOURCE_HOME:=/arrow}
  ^--------------------------^ SC2223 (info): This default assignment may cause DoS due to globbing. Quote it.


In ci/scripts/r_install_system_dependencies.sh line 25:
if [ "`which dnf`" ]; then
      ^---------^ SC2006 (style): Use $(...) notation instead of legacy backticks `...`.

Did you mean:
if [ "$(which dnf)" ]; then


In ci/scripts/r_install_system_dependencies.sh line 27:
elif [ "`which yum`" ]; then
        ^---------^ SC2006 (style): Use $(...) notation instead of legacy backticks `...`.

Did you mean:
elif [ "$(which yum)" ]; then


In ci/scripts/r_install_system_dependencies.sh line 29:
elif [ "`which zypper`" ]; then
        ^------------^ SC2006 (style): Use $(...) notation instead of legacy backticks `...`.

Did you mean:
elif [ "$(which zypper)" ]; then


In ci/scripts/r_install_system_dependencies.sh line 31:
elif [ "`which apk`" ]; then
        ^---------^ SC2006 (style): Use $(...) notation instead of legacy backticks `...`.

Did you mean:
elif [ "$(which apk)" ]; then


In ci/scripts/r_install_system_dependencies.sh line 59:
  if [ "$ARROW_S3" == "ON" ] && [ -f "${ARROW_SOURCE_HOME}/ci/scripts/install_minio.sh" ] && [ "`which wget`" ]; then
                                                                                                ^----------^ SC2006 (style): Use $(...) notation instead of legacy backticks `...`.

Did you mean:
  if [ "$ARROW_S3" == "ON" ] && [ -f "${ARROW_SOURCE_HOME}/ci/scripts/install_minio.sh" ] && [ "$(which wget)" ]; then

For more information:
  https://www.shellcheck.net/wiki/SC2223 -- This default assignment may cause...
  https://www.shellcheck.net/wiki/SC2006 -- Use $(...) notation instead of le...