t0612: add tests to exercise Git/JGit reftable compatibility #15

Job	Run time
config	3s
fuzz smoke test	36s
win+VS build	0s
linux32 (daald/ubuntu32:xenial)	1m 49s
linux-musl (alpine)	1m 51s
pedantic (fedora)	2m 2s
documentation	8s
linux-asan-ubsan (ubuntu-latest)	6s
linux-gcc (ubuntu-20.04)	7s
linux-gcc-default (ubuntu-latest)	6s
linux-leaks (ubuntu-latest)	8s
linux-reftable (ubuntu-latest)	5s
linux-reftable-leaks (ubuntu-latest)	6s
linux-sha256 (ubuntu-latest)	6s
linux-TEST-vars (ubuntu-20.04)	7s
osx-clang (macos-13)	1m 22s
osx-gcc (macos-13)	2m 1s
osx-reftable (macos-13)	1m 10s
sparse	2m 23s
static-analysis	11s
win build	6m 51s
win+VS test	0s
win test (1)	26s
win test (0)	17s
win test (2)	17s
win test (3)	26s
win test (4)	24s
win test (5)	17s
win test (6)	24s
win test (7)	17s
win test (9)	19s
win test (8)	17s
	24m 42s

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