Update test baselines.

Author: peterhuene

crates/wac-graph/tests/graphs/export-already-exists/error.txt

@@ -1,4 +1,4 @@
 failed to export node 0 in export 1 for test case `export-already-exists`
 
 Caused by:
-    export name `foo` already exists in the graph
+    an export with the name `foo` already exists

crates/wac-graph/tests/graphs/implicit-import-conflict/error.txt

@@ -1,4 +1,4 @@
 failed to encode the graph
 
 Caused by:
-    an instantiation of package `test:foo` implicitly imports an item named `foo`, but it conflicts with an explicit import node of the same name
+    an instantiation of package `test:foo` implicitly imports an item named `foo`, but it conflicts with an explicit import of the same name

crates/wac-graph/tests/graphs/invalid-export-name/error.txt

@@ -1,5 +1,5 @@
 failed to export node 0 in export 0 for test case `invalid-export-name`
 
 Caused by:
-    0: export name `!` is not a valid extern name
+    0: export name `!` is not valid
     1: `!` is not in kebab case

crates/wac-graph/tests/graphs/invalid-import-name/error.txt

@@ -1,5 +1,5 @@
 failed to add import node 0 for test case `invalid-import-name`
 
 Caused by:
-    0: import name `NOT_VALID` is not a valid extern name
+    0: import name `NOT_VALID` is not valid
     1: `NOT_VALID` is not in kebab case