Bump git to v2.26.2

Change-Id: I17c4087d9019c2ccebdee1b462d13f79c47d03ea
diff --git a/jenkins-docker/slave-debian/Makefile b/jenkins-docker/slave-debian/Makefile
index 965d9a1..1c5c699 100644
--- a/jenkins-docker/slave-debian/Makefile
+++ b/jenkins-docker/slave-debian/Makefile
@@ -1,7 +1,7 @@
 NO_CACHE ?= false
 IMAGE=gerritforge/gerrit-ci-slave-debian
 MAVEN_VER=3.6.3
-GIT_VER=2.24.0
+GIT_VER=2.26.2
 
 build: build_stretch build_buster