Avoid modifying files in version control when Makefile.PL is rn

.gitignore

@@ -7,3 +7,4 @@ blib/
 t/tmp/
 *.tar.gz
 MYMETA.*
+/lib/RT/Extension/SLA/Test.pm

MANIFEST

@@ -25,7 +25,7 @@ lib/RT/Condition/SLA_RequireDefault.pm
 lib/RT/Condition/SLA_RequireDueSet.pm
 lib/RT/Condition/SLA_RequireStartsSet.pm
 lib/RT/Extension/SLA.pm
-lib/RT/Extension/SLA/Test.pm
+lib/RT/Extension/SLA/Test.pm.in
 lib/RT/Queue_SLA.pm
 Makefile.PL
 MANIFEST			This list of files

Makefile.PL

@@ -22,6 +22,9 @@ substitute(
         RT_BIN_PATH  => $bin_path,
         RT_SBIN_PATH => $sbin_path,
     },
+    {
+        sufix => '.in',
+    },
     qw(lib/RT/Extension/SLA/Test.pm),
 );