inlining: fix the joint_effects calculation (#50117)

There are cases when `joint_effects` already has `:nothrow` tainted while the matches are
fully covered.

Author: aviatesk

base/compiler/abstractinterpretation.jl

@@ -2441,11 +2441,9 @@ function abstract_eval_globalref(interp::AbstractInterpreter, g::GlobalRef, fram
     nothrow = false
     if isa(rt, Const)
         consistent = ALWAYS_TRUE
+        nothrow = true
         if is_mutation_free_argtype(rt)
             inaccessiblememonly = ALWAYS_TRUE
-            nothrow = true
-        else
-            nothrow = true
         end
     elseif isdefined_globalref(g)
         nothrow = true

base/compiler/ssair/inlining.jl

@@ -1401,7 +1401,7 @@ function compute_inlining_cases(@nospecialize(info::CallInfo), flag::UInt8, sig:
         fully_covered &= split_fully_covered
     end
 
-    joint_effects = Effects(joint_effects; nothrow=fully_covered)
+    fully_covered || (joint_effects = Effects(joint_effects; nothrow=false))
 
     if handled_all_cases && revisit_idx !== nothing
         # we handled everything except one match with unmatched sparams,