Avoid unneeded +x in make_rev_spec_parse_repos

The make_rev_spec_parse_repos fixture script used `chmod 755` to
make a looose object file writable (so it could be corrupted, to
test the treatment of corrupted objects). But this also made it
executable, which was not needed (on any platforms).

This commit changes it from 755 to 644 so that it is still made
writable, but not made executable. (It does not start out being
executable.) This does not affect the results of any tests.

Author: EliahKagan

gix/tests/fixtures/make_rev_spec_parse_repos.sh

@@ -53,8 +53,8 @@ git init --bare blob.corrupt
   echo bnkxmdwz | git hash-object -w --stdin
   oid=$(echo bmwsjxzi | git hash-object -w --stdin)
   oidf=objects/$(oid_to_path "$oid")
-  chmod 755 $oidf
-  echo broken >$oidf
+  chmod 644 -- "$oidf"
+  echo broken >"$oidf"
 
   baseline "cafea"
   baseline "cafea^{object}"
@@ -424,4 +424,4 @@ git init invalid-head
   rm .git/refs/heads/main
   baseline 'HEAD'
   baseline 'HEAD:file'
-)
+)