Fix rebuild-ui.sh script (jaegertracing#6098)

## Which problem is this PR solving?
- Resolves jaegertracing#6097

## Description of the changes
- run `git fetch --unshallow` only on shallow repos

## How was this change tested?
- 

## Checklist
- [X] I have read
https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
- [X] I have signed all commits
- [ ] I have added unit tests for the new functionality
- [ ] I have run lint and test steps successfully
  - for `jaeger`: `make lint test`
  - for `jaeger-ui`: `yarn lint` and `yarn test`

---------

Signed-off-by: Andreas Gerstmayr <[email protected]>
Signed-off-by: Yuri Shkuro <[email protected]>
Co-authored-by: Yuri Shkuro <[email protected]>

Author: andreasgerstmayr

scripts/rebuild-ui.sh

@@ -7,7 +7,10 @@ set -euxf -o pipefail
 
 cd jaeger-ui
 
-git fetch --all --unshallow --tags
+if [[ "$(git rev-parse --is-shallow-repository)" == "true" ]]; then
+    git fetch --unshallow
+fi
+git fetch --all --tags
 git log --oneline --decorate=full -n 10 | cat
 
 last_tag=$(git describe --tags --dirty 2>/dev/null)