Fix the syntax in if_else.sh

[certik]

The test script if_else.sh has incorrect syntax for an if statement:

$ bash if_else.sh
if_else.sh: line 2: syntax error near unexpected token `then'
if_else.sh: line 2: `if [[ $FOO -eq 1 ]] then'

The correct syntax uses ; before then.

Unfortunately this correct syntax does not parse:

Syntax error:   × Failed to parse input
  ╰─▶ Failure to parse at Pos((2, 16))
   ╭────
 1 │ if [[ $FOO -eq 1 ]]; then
   ·                ┬
   ·                ╰── expected TILDE_PREFIX, UNQUOTED_ESCAPE_CHAR, SUB_COMMAND, or EXIT_STATUS
   ╰────
  help: expected TILDE_PREFIX, UNQUOTED_ESCAPE_CHAR, SUB_COMMAND,
        or EXIT_STATUS