Fixed crash in bt_service_node when the service is not available in time

[JayHerpin]

---

Basic Info

Info	Please fill out this column
Ticket(s) this addresses	none
Primary OS tested on	to be honest, I haven't tested this.
Robotic platform tested on	untested
Does this PR contain AI generated software?	no
Was this PR description generated by AI software?	no

---

Description of contribution in a few bullet points

• This fixes a crash in the bt_service_node that triggers when a service is not ready in time.
• The problem is just a silly mistake that inadvertently calls constructor 4 on this page: https://en.cppreference.com/w/cpp/string/basic_string/basic_string.html

Description of how this change was tested

• To be honest, it wasn't tested. However, I saw this crash on the jazzy branch and noticed the bug is still present on main. Rather than open an issue, I figured I'd just throw up this trivial patch.

For Maintainers:

• Check that any new parameters added are updated in docs.nav2.org
• Check that any significant change is added to the migration guide
• Check that any new features OR changes to existing behaviors are reflected in the tuning guide
• Check that any new functions have Doxygen added
• Check that any new features have test coverage
• Check that any new plugins is added to the plugins page
• If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists
• Should this be backported to current distributions? If so, tag with backport-*.

[SteveMacenski]

@JayHerpin please sign off DCO. I'll also backport this - thanks!

[JayHerpin]

Correct me if I am wrong, but I don't believe that system_build check failure is anything to do with my changes?

[SteveMacenski]

@JayHerpin pull in main / rebase and it should pass now!

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ree/include/nav2_behavior_tree/bt_service_node.hpp	0.00%	2 Missing ⚠️

Files with missing lines	Coverage Δ
...ree/include/nav2_behavior_tree/bt_service_node.hpp	82.85% <0.00%> (-1.21%)	⬇️

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.