shield Base.require from invalidations when loading Symbolics.jl (#49604)

(cherry picked from commit 5039d8a)

Author: KristofferC

base/loading.jl

@@ -747,10 +747,10 @@ function explicit_project_deps_get(project_file::String, name::String)::Union{No
     return nothing
 end
 
-function is_v1_format_manifest(raw_manifest::Dict)
+function is_v1_format_manifest(raw_manifest::Dict{String})
     if haskey(raw_manifest, "manifest_format")
         mf = raw_manifest["manifest_format"]
-        if mf isa Dict && haskey(mf, "uuid")
+        if mf isa Dict{String} && haskey(mf, "uuid")
             # the off-chance where an old format manifest has a dep called "manifest_format"
             return true
         end