Test suite: activate a temp project if we need to install Aqua.jl during the test suite (#425)

Author: DilumAluthge

test/ambiguous.jl

@@ -5,6 +5,7 @@
 original_depot_path = copy(Base.DEPOT_PATH)
 original_load_path = copy(Base.LOAD_PATH)
 original_env = copy(ENV)
+original_project = Base.active_project()
 ###
 
 import Pkg
@@ -13,6 +14,7 @@ import Pkg
 if Base.find_package("Aqua") === nothing
     @debug "Installing Aqua.jl for SparseArrays.jl tests"
     iob = IOBuffer()
+    Pkg.activate(; temp = true)
     try
         # TODO: make this version tie to compat in Project.toml
         # or do this another safer way
@@ -103,4 +105,6 @@ end
 for (k, v) in pairs(original_env)
     ENV[k] = v
 end
+
+Base.set_active_project(original_project)
 ###