Tests: Don't remove a parent of $PWD

Solaris/OpenIndiana/Illumos `rm` checks that and errors out.

In these cases we don't actually need it to be a part of $PWD as
it's just for cleanup, so we `cd` out before.

See #5472
See 1ee57e92447781b5ff79aaa7c55f6468fc84a37d
Fixes #6555
Fixes #6558

(cherry picked from commit 9cbd3d57a01ba8f4813febff83210f595518cea1)

tests/checks/cd.fish

@@ -19,8 +19,8 @@ begin
     cd x
     pwd
 end
-rm -rf $tmp
 cd $oldpwd
+rm -rf $tmp
 
 # Create a test directory to store our stuff.
 set -l base /tmp/cdcomp_test

tests/checks/wildcard.fish

@@ -2,6 +2,7 @@
 
 # Ensure that, if variable expansion results in multiple strings
 # and one of them fails a glob, that we don't fail the entire expansion.
+set -l oldpwd (pwd)
 set dir (mktemp -d)
 cd $dir
 mkdir a
@@ -12,4 +13,5 @@ set dirs ./a ./b
 echo $dirs/*.txt
 # CHECK: ./b/file.txt
 
+cd $oldpwd
 rm -Rf $dir