gitignore: ignore upload-artefacts (#30325)

Our `WriteArchive`, used by ci builder, creates files in the repo root,in order to upload. After we've built the amd64-builds, we create the uploads, and cause the repo to be flagged as dirty for the remaining builds.

This change fixes it by adding the artefacts to gitignore. Closes #30324

.gitignore

@@ -28,6 +28,9 @@ build/_vendor/pkg
 /build/bin/
 /geth*.zip
 
+# used by the build/ci.go archive + upload tool
+/geth*.tar.gz
+
 # travis
 profile.tmp
 profile.cov