fix: fetch entire change and integration history

Fetching with a specific depth is insufficient and finding the
merge-base is still prone to fail because Git can't resolve the history
between the grafted refspec we start with and whatever the integration
branch is.

Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
Change-Id: Ie70905f6f5c651022b3ff9e1e56d2eb2177ed7ce
(cherry picked from commit afdcff720185959585c2a1ef970f2caa755e6682)
diff --git a/script/static-checks/static-checks.sh b/script/static-checks/static-checks.sh
index 1424349..5e9edbb 100755
--- a/script/static-checks/static-checks.sh
+++ b/script/static-checks/static-checks.sh
@@ -30,7 +30,7 @@
         fi
     fi
 
-    git fetch --depth=100 origin "$GERRIT_REFSPEC"
+    git fetch --unshallow --update-shallow origin "$GERRIT_REFSPEC"
     git checkout FETCH_HEAD
 
     merge_base=$(get_merge_base)