scripts/oe-setup-layers: Update how to determine if directory is git repo

Previously _is_repo_git_repo() would return a result containing b'true\n' or
b'false\n' if 'git rev-parse' ran successfully, instead of True of False.

While this can be solved using e.g. result.strip().decode("utf-8") == "true",
there are some other cases to consider.
First, .git can be a file and not a directory when using a worktree.
Second, an emtpy .git directory in 'repodir' for which some parent of
'repodir' is an actual git repo will still return True in this case.

To account for these cases as well, use 'git rev-parse --show-toplevel'
and compare the result against 'repodir' instead of
using 'git rev-parse --is-inside-git-dir'.

(From OE-Core rev: 0830f53900dd7fd669a7d6492325559ad3225302)

Signed-off-by: Jermain Horsman <jermain.horsman@nedap.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/oe-setup-layers

@@ -20,13 +20,13 @@ import os
 import subprocess
 
 def _is_repo_git_repo(repodir):
-    git_dir = os.path.join(repodir, ".git")
-    if not os.access(git_dir, os.R_OK):
-        return False
     try:
-        return subprocess.check_output("git -C %s rev-parse --is-inside-git-dir" % git_dir, shell=True, stderr=subprocess.DEVNULL)
+        curr_toplevel = subprocess.check_output("git -C %s rev-parse --show-toplevel" % repodir, shell=True, stderr=subprocess.DEVNULL)
+        if curr_toplevel.strip().decode("utf-8") == repodir:
+            return True
     except subprocess.CalledProcessError:
-        return False
+        pass
+    return False
 
 def _is_repo_at_rev(repodir, rev):
     try: