Remove extraneous {{end}} in post upgrade template

[cbosdo]

What does this PR change?

Fix runtime panic:

panic: template: script:18: unexpected {{end}}

goroutine 1 [running]:
text/template.Must(...)
        /usr/lib64/go/1.21/src/text/template/helper.go:26
github.com/uyuni-project/uyuni-tools/mgradm/shared/templates.PostUpgradeTemplateData.Render({{0x8e118b?, 0x241?}}, {0x9a6ae0, 0xc0003aa098})
        /home/abuild/rpmbuild/BUILD/uyuni-tools-git-24.1c27fac/mgradm/shared/templates/postUpgradeScriptTemplate.go:39 +0x173
github.com/uyuni-project/uyuni-tools/shared/utils.WriteTemplateToFile({0x9a79a0, 0xc00038e8b0}, {0xc000396540, 0x25}, 0x396526?, 0xc0?)
        /home/abuild/rpmbuild/BUILD/uyuni-tools-git-24.1c27fac/shared/utils/template.go:36 +0x1b7

Test coverage

• No tests: add explanation

• No tests: already covered

• Unit tests were added

• DONE

Links

Issue(s): #

• DONE

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