ci: use make in PRs

[axw]

Use Make targets, so CI behaves more like developer environments. This ensures license headers are checked in PRs.

Also, tidy up the Makefile a little:

• zip now depends on build. This ensures a make zip in isolation won't zip a stale build and confuse unsuspecting people like me.
• replace gen-notice with a non-PHONY NOTICE.txt target, by depending on go.mod

[ghost]

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• Start Time: 2022-08-12T08:08:59.997+0000

• Duration: 8 min 32 sec

Test stats 🧪

Test	Results
Failed	0
Passed	130
Skipped	32
Total	162

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[kruskall]

Thanks! LGTM!