Fix plotattributes in _add_plot_title! (#4090)

Co-authored-by: Simon Christ <SimonChrist@gmx.de>

test/runtests.jl

@@ -37,19 +37,25 @@ end
     Plots.use_local_dependencies[] = temp
 end
 
-include("test_defaults.jl")
-include("test_pipeline.jl")
-include("test_axes.jl")
-include("test_layouts.jl")
-include("test_contours.jl")
-include("test_axis_letter.jl")
-include("test_components.jl")
-include("test_shorthands.jl")
-include("integration_dates.jl")
-include("test_recipes.jl")
-include("test_hdf5plots.jl")
-include("test_pgfplotsx.jl")
-include("test_plotly.jl")
+for fn in (
+    "test_defaults.jl",
+    "test_pipeline.jl",
+    "test_axes.jl",
+    "test_layouts.jl",
+    "test_contours.jl",
+    "test_axis_letter.jl",
+    "test_components.jl",
+    "test_shorthands.jl",
+    "integration_dates.jl",
+    "test_recipes.jl",
+    "test_hdf5plots.jl",
+    "test_pgfplotsx.jl",
+    "test_plotly.jl",
+)
+    @testset "$fn" begin
+        include(fn)
+    end
+end
 
 reference_dir(args...) =
     joinpath(homedir(), ".julia", "dev", "PlotReferenceImages", args...)

test/test_layouts.jl

@@ -25,3 +25,10 @@ end
     @test pl[:plot_title] == "My new title"
     @test pl[:plot_titleindex] == 5
 end
+
+@testset "Plots.jl/issues/4083" begin
+    p = plot(plot(1:2), plot(1:2); border = :grid, plot_title = "abc")
+    @test p[1][:framestyle] === :grid
+    @test p[2][:framestyle] === :grid
+    @test p[3][:framestyle] === :none
+end