Fixes issue with go-licenses generating empty report due to module vendoring (#3996)

# Summary

It was observed in the past that sometimes the `licenses.csv` file is
generated empty. Finally found the issue, it was due to vendoring of the
go modules. `go-licenses` could not handle it correctly and added this
kind of entry every time the module was found in the vendor folder. This
is also reported as an issue in
google/go-licenses#178

```
github.com/davecgh/go-spew/spew,Unknown,https://github.com/10gen/ops-manager-kubernetes/blob/HEAD/vendor/github.com/davecgh/go-spew/LICENSE,ISC
github.com/emicklei/go-restful/v3,Unknown,https://github.com/10gen/ops-manager-kubernetes/blob/HEAD/vendor/github.com/emicklei/go-restful/v3/LICENSE,MIT
github.com/evanphx/json-patch/v5,Unknown,https://github.com/10gen/ops-manager-kubernetes/blob/HEAD/vendor/github.com/evanphx/json-patch/v5/LICENSE,BSD-3-Clause
```

By adding `GOFLAGS="-mod=mod"` we completely omit vendor folder and
switch back to `go.mod`.

## Documentation changes

* [ ] Add an entry to [release notes](.../RELEASE_NOTES.md).
* [ ] When needed, make sure you create a new [DOCSP
ticket](https://jira.mongodb.org/projects/DOCSP) that documents your
change.

## Changes to CRDs

* [ ] Add `slaskawi`(Sebastian) and `@giohan` (George) as reviewers.
* [ ] Make sure any changes are reflected on `/public/samples`
directory.

Author: MaciejKaras

scripts/evergreen/update_licenses.sh

@@ -20,7 +20,7 @@ process_licenses() {
         return 1
     fi
 
-    PATH=$GOPATH/bin:$PATH GOOS=linux GOARCH=amd64 go-licenses report . --template "$SCRIPTS_DIR/update_licenses.tpl" > licenses_full.csv 2> licenses_stderr  || true
+    PATH=$GOPATH/bin:$PATH GOOS=linux GOARCH=amd64 GOFLAGS="-mod=mod" go-licenses report . --template "$SCRIPTS_DIR/update_licenses.tpl" > licenses_full.csv 2> licenses_stderr  || true
 
     # Filter and sort the licenses report
     grep -v 10gen licenses_full.csv | grep -v "github.com/mongodb" | grep -v "^golang.org" | sort > licenses.csv || true