test-lib-functions: fix test_subcommand_inexact

The implementation of test_subcommand_inexact() was originally
introduced in e4d0c11 (repack: respect kept objects with '--write-midx
-b', 2021-12-20) with the intention to allow finding a subcommand based
on an initial set of arguments. The inexactness was intended as a way to
allow flexible options beyond that initial set, as opposed to
test_subcommand() which requires that the full list of options is
provided in its entirety.

The implementation began by copying test_subcommand() and replaced the
repeated argument 'printf' statement to append ".*" instead of "," to
each argument. This has a few drawbacks:

1. Most importantly, this repeats the use of ".*" within 'expr', so the
   inexact match is even more flexible than expected. It allows the list
   of arguments to exist as a subsequence (with any other items included
   between those arguments).

2. The line 'expr="$(expr%,}"' that previously removed a trailing comma
   now no longer does anything, since the string ends with ".*".

Both of these issues are fixed by keeping the addition of the comma in
the printf statement, then adding ".*" after stripping out the trailing
comma.

All existing tests continue to pass with this change. There was one
instance from t7700-repack.sh that was taking advantage of this
flexibility, but it was removed in the previous change.

Helped-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>

t/test-lib-functions.sh

@@ -1811,8 +1811,8 @@ test_subcommand_inexact () {
 		shift
 	fi
 
-	local expr=$(printf '"%s".*' "$@")
-	expr="${expr%,}"
+	local expr=$(printf '"%s",' "$@")
+	expr="${expr%,}.*"
 
 	if test -n "$negate"
 	then