Exclude .github in rat files (#550)

diff --git a/dev/release/rat_exclude_files.txt b/dev/release/rat_exclude_files.txt
index d64a431..c5435d0 100644
--- a/dev/release/rat_exclude_files.txt
+++ b/dev/release/rat_exclude_files.txt
@@ -12,3 +12,4 @@
 rat.txt
 # auto-generated
 arrow-flight/src/arrow.flight.protocol.rs
+.github/*