test libs: rename bundle helper to "lib-bundle.sh"

Rename the recently introduced test-bundle-functions.sh to be
consistent with other lib-*.sh files, which is the convention for
these sorts of shared test library functions.

The new test-bundle-functions.sh was introduced in 9901164d81 (test:
add helper functions for git-bundle, 2021-01-11). It was the only
test-*.sh of this nature.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5510-fetch.sh

@@ -9,7 +9,7 @@ GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
-. "$TEST_DIRECTORY"/test-bundle-functions.sh
+. "$TEST_DIRECTORY"/lib-bundle.sh
 
 D=$(pwd)
 

t/t6020-bundle-misc.sh

@@ -9,7 +9,7 @@ GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
-. "$TEST_DIRECTORY"/test-bundle-functions.sh
+. "$TEST_DIRECTORY"/lib-bundle.sh
 
 # Create a commit or tag and set the variable with the object ID.
 test_commit_setvar () {