opam repo add triggers a git-maintenance race condition

[kit-ty-kate]

I noticed a type of error locally (as well as in CI from time to time, i think):

diff --git a/tests/reftests/legacy-git.test b/tests/reftests/legacy-git.test
index 3dbd569da..c7942b61b 100644
--- a/tests/reftests/legacy-git.test
+++ b/tests/reftests/legacy-git.test
@@ -1370,24 +1370,11 @@ P4.3
 PASS 1
 ### : REPO :
 ### opam repo add REPO2 REPO -k git
-[REPO2] Initialised
-[WARNING] The repository 'REPO2' at git+file://${BASEDIR}/REPO doesn't have a 'repo' file, and might not be compatible with this version of opam.
-[NOTE] Repository at git+file://${BASEDIR}/REPO doesn't define its version, assuming it's 1.2.
-
-<><> Upgrading repositories from older opam format ><><><><><><><><><><><><><><>
-Upgrading repository "REPO2"...
-Updated ${BASEDIR}/OPAM/repo/REPO2/packages/P1.0/opam
-Updated ${BASEDIR}/OPAM/repo/REPO2/packages/P1.1/opam
-Updated ${BASEDIR}/OPAM/repo/REPO2/packages/P2.1/opam
-Updated ${BASEDIR}/OPAM/repo/REPO2/packages/P3.1~weird-version.test/opam
-Updated ${BASEDIR}/OPAM/repo/REPO2/packages/P4.1/opam
-Updated ${BASEDIR}/OPAM/repo/REPO2/packages/P4.2/opam
-Updated ${BASEDIR}/OPAM/repo/REPO2/packages/P4.3/opam
-Updated ${BASEDIR}/OPAM/repo/REPO2/packages/P5.1/opam
-[NOTE] Repository REPO2 has been added to the selections of switch 10+a+b only.
-       Run `opam repository add REPO2 --all-switches|--set-default' to use it in all existing switches, or in newly created switches, respectively.
-
+[ERROR] Could not update repository "REPO2": ${OPAM}: "lstat" failed on ${BASEDIR}/OPAM/repo/REPO2/.git/objects/maintenance.lock: No such file or directory
+[ERROR] Initial repository fetch failed
+# Return code 40 #
 ### opam repo remove REPO2 --all
+[WARNING] No configured repositories by these names found: REPO2
 ### opam repo remove test --all
 ### : LIST :
 ### opam list -A

There seems to be two problems:

• some kind of race condition with git
• opam repo add shouldn't scan the .git directory but apparently does

[kit-ty-kate]

Similarly

diff --git a/_build/default/tests/reftests/action-disk.test b/_build/default/tests/reftests/action-disk.out
old mode 100755
new mode 100644
index f65d63f..75d3a66
--- a/_build/default/tests/reftests/action-disk.test
+++ b/_build/default/tests/reftests/action-disk.out
@@ -1748,6 +1748,7 @@ Processing  1/1:
 + git "-C" "${BASEDIR}/OPAM/install-from-git-pin-all/.opam-switch/sources/main-gpin" "clean" "-fdx"
 + git "-C" "${BASEDIR}/OPAM/install-from-git-pin-all/.opam-switch/sources/main-gpin" "remote" "set-url" "origin" "file://${BASEDIR}/main-gpin"
 + git "-C" "${BASEDIR}/OPAM/install-from-git-pin-all/.opam-switch/sources/main-gpin" "fetch" "-q" "file://${BASEDIR}/main-gpin" "--update-shallow" "+master:refs/remotes/opam-ref-master"
+- warning: unable to unlink '${BASEDIR}/OPAM/install-from-git-pin-all/.opam-switch/sources/main-gpin/.git/objects/maintenance.lock': Permission denied
 + git "-C" "${BASEDIR}/OPAM/install-from-git-pin-all/.opam-switch/sources/main-gpin" "diff" "--no-ext-diff" "--quiet" "refs/remotes/opam-ref-master" "--"
 + git "-C" "${BASEDIR}/OPAM/install-from-git-pin-all/.opam-switch/sources/main-gpin" "submodule" "status" "--recursive"
 + git "-C" "${BASEDIR}/OPAM/install-from-git-pin-all/.opam-switch/sources/main-gpin" "clean" "-fdx"
File "tests/reftests/action-disk.test", line 1, characters 0-0:
/usr/bin/git --no-pager diff --no-index --color=always -u _build/default/tests/reftests/action-disk.test _build/default/tests/reftests/action-disk.out
Command exited with code 1.