fix: pass absolute path to pam_smoke_test via meson.current_build_dir()

dlopen with a bare filename searches LD_LIBRARY_PATH/ld.so cache, not the
build dir. Using the explicit absolute path avoids the lookup failure.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

meson.build

@@ -91,4 +91,6 @@ pam_smoke = executable(
   dependencies: [cc.find_library('dl', required: true)]
 )
 
-test('pam symbols', pam_smoke, args: [pam_cargo[0]])
+test('pam symbols', pam_smoke,
+     args: [meson.current_build_dir() / 'libahfail_pam.so'],
+     depends: pam_cargo)