ci(*-leaks): skip the git-svn tests to save time

I noticed recently that the leak-checking jobs still take a lot of time,
and upon analysis, the git-svn tests contribute significantly to this.

Analyzing a recent CI run, I saw that the Git test suite contains
1,017 tests, running for approximately 5¼ hours total. Of these, 65
git-svn-related tests (~6% of test count) took 42.24 minutes combined,
accounting for ~13.% of the total runtime. This implies that the git-svn
tests are roughly twice as expernsive compared to the other tests.

However, testing git-svn in the leak-checking jobs provides minimal
value: git-svn is implemented as a Perl script, and leak checking only
handles C code. While git-svn does call into Git's built-in commands
that are implemented in C, these are standard Git operations that are
already thoroughly exercised elsewhere in the test suite. Therefore,
running the git-svn tests in the leak-checking jobs only adds to the
overall run time with little value in return.

Given that the leak-checking jobs are particularly time-intensive and
these 42+ minutes of SVN tests per job provide no additional leak
detection value, skip them in the *-leaks jobs to reduce CI runtime.

Assisted-by: Claude Sonnet 4.5
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: dscho

ci/lib.sh

@@ -356,6 +356,7 @@ linux-musl-meson)
 	;;
 linux-leaks|linux-reftable-leaks)
 	export SANITIZE=leak
+	export NO_SVN_TESTS=LetsSaveSomeTime
 	;;
 linux-asan-ubsan)
 	export SANITIZE=address,undefined