scripts: use trap to make sure old files always restored

[Roasbeef]

In this commit, we fix an issue I observed on my machine after updating many command line/dev utilities.

I observed that if the script failed for w/e reason, then the old files weren't properly restored.

The repro on my machine is something like:

1. Shutdown docker, make sure the daemon isn't accessible.
2. Run mac sqlc. The script should fail.
3. Observe that the files in your local working tree are still altered.

We fix this by using the trap command, which is basically like Go's defer, but for bash
scripts!

[coveralls]

Pull Request Test Coverage Report for Build 11789125409

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 12 unchanged lines in 5 files lost coverage.
• Overall coverage remained the same at 40.658%

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Files with Coverage Reduction	New Missed Lines	%
tappsbt/create.go	2	53.22%
internal/test/helpers.go	2	86.85%
commitment/tap.go	2	84.43%
asset/asset.go	2	80.2%
tapgarden/caretaker.go	4	68.5%

Totals
Change from base Build 11782733093:	0.0%
Covered Lines:	24691
Relevant Lines:	60728

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💛 - Coveralls

[jharveyb]

LGTM 👍🏽