When only one resource is individually selected, do not write '1 resource selected' because it's confusing

[marcellamaki]

Summary

Description of the change(s) you made

Fixes #4649

Manual verification steps performed

Confirmed that on any individual editing action modal, '1 resource selected' does not appear at the top of the modal

Screenshots (if applicable)

Example
Now

Previous

Does this introduce any tech-debt items?

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Reviewer guidance

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Are there any risky areas that deserve extra testing?

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[rtibbles]

Manual testing checks out, and no regression when multiple resources are selected.

Only other use of this string is in the import from channels flow, where it seems more appropriate.

[pcenov]

LGTM!