build: fix formatting --disable-sandbox-check

Make it match the other `AC_ARG_ENABLE` code.

This amends commit a53de49 ("build: improve --disable-sandbox-check
help string", 2025-01-13).

Relates to #6592.

configure.ac

@@ -72,9 +72,9 @@ AS_IF([test "x$enable_sanitizer" != "xno" ], [
 HAVE_SANDBOX_CHECK=""
 AC_SUBST([HAVE_SANDBOX_CHECK])
 AC_ARG_ENABLE([sandbox-check],
-        [AS_HELP_STRING([--disable-sandbox-check],
-            [disable checking if firejail is running within a sandbox, only use
-             this when developing firejail inside of a sandbox])])
+    [AS_HELP_STRING([--disable-sandbox-check],
+        [disable checking if firejail is running within a sandbox, only use
+         this when developing firejail inside of a sandbox])])
 AS_IF([test "x$enable_sandbox_check" != "xno"], [
 	HAVE_SANDBOX_CHECK="-DHAVE_SANDBOX_CHECK"
 ])