Postgres integration test is flaky

[Gerrit91]

Description

We had this already in the past but much more often. It still happens here and then:

 === RUN   Test_Postgres_Restore
    main_test.go:68: running restore flow
    main_test.go:77: running cleanup
    main_test.go:95: applying resource manifests
    main_test.go:114: adding test data to database
    main_test.go:118: taking a backup
    main_test.go:125: 
        	Error Trace:	/home/runner/work/backup-restore-sidecar/backup-restore-sidecar/integration/main_test.go:125
        	            				/home/runner/work/backup-restore-sidecar/backup-restore-sidecar/integration/postgres_test.go:21
        	Error:      	Received unexpected error:
        	            	rpc error: code = Internal desc = error creating backup: a backup is already in progress
        	Test:       	Test_Postgres_Restore