Spotinst: Don't skip LB attachments when SpotinstHybrid is enabled

[liranp]

This PR resolves an issue with LB attachments of non-Spotinst managed instance groups. LB attachments shouldn't be skipped entirely when the SpotinstHybrid feature is enabled.

[hakman]

@liranp do you know if this fixes #10908?

[liranp]

@hakman Unfortunately, it doesn't, but I'll submit another PR later today to fix that issue as well.

[hakman]

No worries. Thanks!

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[liranp]

/retest

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[estahn]

@liranp Thanks for the quick turnaround!
@hakman Thanks for approving it.

[estahn]

@liranp @hakman Can we get this into the next 1.19 release?

[liranp]

@estahn You can work around it temporarily by downloading v1.19.1 from our fork.

[hakman]

I am not opposed to cherry-picking bug fixes to 1.19, but would leave it to @liranp to decide what and how.