Fix typo of substitutions in unit tests
Fix typo of substitutions in unit tests

Signed-off-by: David Vo <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@vovo.id.au>

matrix-org/matrix-appservice-slack,matrix-org/matrix-appservice-slack,matrix-org/matrix-appservice-slack,matrix-org/matrix-appservice-slack