send group subscription welcome email only if template is enabled

[kurund]

Fixes: https://lab.civicrm.org/dev/core/-/issues/3162

[civibot]

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[jaapjansma]

test this please

[jaapjansma]

• General standards
  • Explain (r-explain)
    • PASS : The goal/problem/solution have been adequately explained in issue.
  • User impact (r-user)
    • PASS: The change would be intuitive or unnoticeable for a majority of users who work with this feature.
  • Documentation (r-doc)
    • PASS: The changes do not require documentation.
  • Run it (r-run)
    • ISSUE: We did test this in the test environment of this PR. Everything seems to work. However the test environment has CIVICRM_MAIL_LOG defined so we are not able to test whether the e-mail gets send or whether it returns in an error.
• Developer standards
  • Technical impact (r-tech)
    • PASS: The change preserves compatibility with existing callers/code/downstream.
  • Code quality (r-code)
    • PASS: The functionality, purpose, and style of the code seems clear+sensible.
  • Maintainability (r-maint)
    • PASS: The change is trivial enough that it does not require tests.
  • Test results (r-test)
    • PASS: The test results are all-clear.

@kurund do you think there is any risk with merging this without testing the actual mail?

[kurund]

@jaapjansma

I have tested with actual mailings and it is working as expected.

[jaapjansma]

@eileenmcnaughton or @colemanw can of you merge this PR? We believe it is safe to merge this.