t0001: ignore ".dirty" suffix on Git version

When testing modifications in Git that affect CGit, it is annoying to
have t0001 failing simply because the Git version has a ".dirty" suffix
when the version of Git there does indeed match that specified in the
CGit makefile.  Stop this by stripping the ".dirty" suffix from the
GIT_VERSION variable.

Note that this brings the "Git version" behaviour in line with the
"submodule version" case which does not check if the working tree in
git/ is modified.

Signed-off-by: John Keeping <john@keeping.me.uk>

tests/t0001-validate-git-versions.sh

@@ -13,7 +13,7 @@ test_expect_success 'extract Git version from Makefile' '
 
 test_expect_success 'test Git version matches Makefile' '
 	( cat ../../git/GIT-VERSION-FILE || echo "No GIT-VERSION-FILE" ) |
-	sed -e "s/GIT_VERSION[ 	]*=[ 	]*//" >git_version &&
+	sed -e "s/GIT_VERSION[ 	]*=[ 	]*//" -e "s/\\.dirty$//" >git_version &&
 	test_cmp git_version makefile_version
 '