Stabilise left panel tests

[RussKie]

FormBrowse gets closed before information required for the left panel is loaded, e.g. here's a log from a test:

Test log

> git init
Initialized empty Git repository in C:/Users/appveyor/AppData/Local/Temp/1/xqimufdy.lc1/repo1/.git/

> git rev-parse --git-common-dir
.git

> git config core.safecrlf false

GitModuleTestHelper initialised at C:\Users\appveyor\AppData\Local\Temp\1\xqimufdy.lc1\repo1
Created commit: ee7d2e2b6854cdf3c50f36d9e1029317bbdee4a0, message: A commit message
> git remote add "remote1" "http://localhost/remotes/remote1.git"

> git remote add "remote5" "http://localhost/remotes/remote5.git"

> git remote add "remote3" "http://localhost/remotes/remote3.git"

> git remote add "remote4" "http://localhost/remotes/remote4.git"

> git remote add "remote2" "http://localhost/remotes/remote2.git"

> git remote rm "remote5"

> git rev-parse HEAD
> git --no-optional-locks for-each-ref --format="%(objectname) %(refname)" refs/heads/
ee7d2e2b6854cdf3c50f36d9e1029317bbdee4a0

> git --no-optional-locks for-each-ref --format="%(if)%(authordate)%(then)%(objectname) %(refname)%(else)%(*objectname) %(*refname)%(end)"
ee7d2e2b6854cdf3c50f36d9e1029317bbdee4a0 refs/heads/master

ee7d2e2b6854cdf3c50f36d9e1029317bbdee4a0 refs/heads/master

> git --no-optional-locks for-each-ref --format="%(objectname) %(refname)" refs/heads/
> git --no-optional-locks for-each-ref --format="%(objectname) %(refname)" refs/remotes/
> git ls-files -z --unmerged

ee7d2e2b6854cdf3c50f36d9e1029317bbdee4a0 refs/heads/master

> git remote -v
> git for-each-ref --format="%(push:track,nobracket)::%(upstream:track,nobracket)::%(push)::%(upstream)::%(refname:short)" refs/heads/

::::::::master

> git for-each-ref --format="%(push:track,nobracket)::%(upstream:track,nobracket)::%(push)::%(upstream)::%(refname:short)" refs/heads/master
remote1	http://localhost/remotes/remote1.git (fetch)
remote1	http://localhost/remotes/remote1.git (push)
remote2	http://localhost/remotes/remote2.git (fetch)
remote2	http://localhost/remotes/remote2.git (push)
remote3	http://localhost/remotes/remote3.git (fetch)
remote3	http://localhost/remotes/remote3.git (push)
remote4	http://localhost/remotes/remote4.git (fetch)
remote4	http://localhost/remotes/remote4.git (push)

> git --no-optional-locks for-each-ref --format="%(objectname) %(refname)" refs/remotes/
::::::::master

> git ls-files -z --unmerged


> git remote
> git --no-optional-locks -c diff.ignoreSubmodules=none status --porcelain=2 -z --untracked-files
GetRemoteNode: loaded 0 nodes
FormBrowse closing
FormBrowse form closing
FormBrowse closed
> git branch --contains ee7d2e2b6854cdf3c50f36d9e1029317bbdee4a0
> git for-each-ref --sort=-taggerdate --format="%(refname)" refs/tags/
> git tag --contains ee7d2e2b6854cdf3c50f36d9e1029317bbdee4a0
> git describe --tags --first-parent --abbrev=40 ee7d2e2b6854cdf3c50f36d9e1029317bbdee4a0
remote1
remote2
remote3
remote4

* master



1 D. N... 100644 000000 000000 8c7e5a667f1b771847fe88c01c3de34413a1b220 0000000000000000000000000000000000000000 A.txt\u0000? A.txt\u0000

GitModuleTestHelper disposing
GitModuleTestHelper disposed
ReferenceRepository disposed

Wait for all async operations to complete before proceeding on to assertions.

Resolves #7743 and all recent test instability