bump github plugin version to 2.1.5 (#22575)

Co-authored-by: Mattermost Build <build@mattermost.com>

server/Makefile

@@ -144,7 +144,7 @@ PLUGIN_PACKAGES += mattermost-plugin-calls-v0.15.1
 PLUGIN_PACKAGES += mattermost-plugin-channel-export-v1.0.0
 PLUGIN_PACKAGES += mattermost-plugin-confluence-v1.3.0
 PLUGIN_PACKAGES += mattermost-plugin-custom-attributes-v1.3.1
-PLUGIN_PACKAGES += mattermost-plugin-github-v2.1.4
+PLUGIN_PACKAGES += mattermost-plugin-github-v2.1.5
 PLUGIN_PACKAGES += mattermost-plugin-gitlab-v1.6.0
 PLUGIN_PACKAGES += mattermost-plugin-jenkins-v1.1.0
 PLUGIN_PACKAGES += mattermost-plugin-jira-v3.2.2