fix(ibm_is_share): 404 error fix on datasource

[uibm]

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Relates OR Closes #0000

Output from acceptance testing:

 % make testacc TEST=./ibm/service/vpc TESTARGS='-run=TestAccIbmIsShareDataSource404'
=== RUN   TestAccIbmIsShareDataSource404
--- PASS: TestAccIbmIsShareDataSource404 (2.70s)
PASS
ok      github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/vpc     4.360s

% make testacc TEST=./ibm/service/vpc TESTARGS='-run=TestAccIbmIsSourceShareDataSource404'
=== RUN   TestAccIbmIsSourceShareDataSource404
--- PASS: TestAccIbmIsSourceShareDataSource404 (3.36s)
PASS
ok      github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/vpc     5.387s

[uibm]