fix branch name

Author: blink1073

.evergreen/scripts/configure-env.sh

@@ -76,7 +76,7 @@ EOT
 rm -rf $DRIVERS_TOOLS
 BRANCH=master
 ORG=mongodb-labs
-BRANCH=fix-mock-kms-header
+BRANCH=fix-mock-kms-headers
 ORG=blink1073
 git clone --branch $BRANCH https://github.com/$ORG/drivers-evergreen-tools.git $DRIVERS_TOOLS