Tests: Run each test in their respective directories

This is so they can find their associated resources and it's
the same behavior as in Lagom.

This also required changing some tests so that they could
write their resources in a writable location.

Userland/Shell/Tests/heredocs.sh

@@ -1,6 +1,8 @@
 #!/bin/sh
 
 source $(dirname "$0")/test-commons.inc
+# go to a writable directory
+cd /tmp
 
 # Simple usage, single doc
 echo <<-test > sh.doc.test
@@ -71,4 +73,6 @@ test
 test2
 
 rm -f sh.doc.test
+# return to original directory
+cd -
 pass

Userland/Shell/Tests/loop.sh

@@ -1,7 +1,8 @@
 #!/bin/sh
 
 source $(dirname "$0")/test-commons.inc
-
+# go to a writable directory
+cd /tmp
 singlecommand_ok=yes
 multicommand_ok=yes
 inlineexec_ok=yes
@@ -95,5 +96,6 @@ if not test \
 
     fail "Something failed :("
 }
-
+# return to original directory
+cd -
 echo PASS