git-artifacts: try creating MINGW-packages.bundle a couple times if needed

In private tests, this command seems to have failed consistently, with
this error message:

    + git commit -s -m 'mingw-w64-git: new version (test)' PKGBUILD
    [test e641948] mingw-w64-git: new version (test)
    1 file changed, 2 insertions(+), 2 deletions(-)
    + git bundle create /d/a/test/test/artifacts/MINGW-packages.bundle 'test^..test'
    error: pack-objects died
    Error: Process completed with exit code 1.

After extensive debugging of this elusive problem (it is relatively
consistent when running inside a workflow step, but running it
interactively via `action-tmate` succeeds every single time), the most
plausible explanation is that Defender doing its thing, and that results
in a "Permission Denied" problem.

Calling the command with `GIT_TRACE2_EVENT` enabled seems to work around
the problem, and just in case it does not, let's add a loop to try a
couple more times should the command fail.

In the end, just validate the bundle to make sure that it was created
correctly.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.github/workflows/git-artifacts.yml

@@ -411,17 +411,35 @@ jobs:
           if test -z "$EXISTING_GIT_TAG"
           then
             git commit -s -m "mingw-w64-git: new version ($version)" PKGBUILD &&
-            git bundle create "$b"/MINGW-packages.bundle \
-              "origin/$RELEASE_BRANCH..$RELEASE_BRANCH"
+            for seconds in 1 3 10 15
+            do
+              GIT_TRACE2_EVENT=1 \
+              git bundle create "$b"/MINGW-packages.bundle \
+                "origin/$RELEASE_BRANCH..$RELEASE_BRANCH" &&
+              break
+              # to ease debugging
+              git bundle verify "$b"/MINGW-packages.bundle ||:
+              sleep $seconds
+            done &&
+            git bundle verify "$b"/MINGW-packages.bundle
           elif ! git update-index --ignore-submodules --refresh ||
             ! git diff-files --ignore-submodules ||
             ! git diff-index --cached --ignore-submodules HEAD
           then
             echo "::warning::Uncommitted changes after build!" >&2 &&
             git diff >&2 &&
             git commit -s -m "mingw-w64-git: new version ($version)" PKGBUILD &&
-            git bundle create "$b"/MINGW-packages.bundle \
-              "$RELEASE_BRANCH^..$RELEASE_BRANCH"
+            for seconds in 1 3 10 15
+            do
+              GIT_TRACE2_EVENT=1 \
+              git bundle create "$b"/MINGW-packages.bundle \
+                "$RELEASE_BRANCH^..$RELEASE_BRANCH" &&
+              break
+              # to ease debugging
+              git bundle verify "$b"/MINGW-packages.bundle ||:
+              sleep $seconds
+            done &&
+            git bundle verify "$b"/MINGW-packages.bundle
           fi)
       - name: Cache ${{env.MINGW_PACKAGE_PREFIX}}-git
         if: steps.restore-cached-git-pkg.outputs.cache-hit != 'true'