Added missing key prop to NoTests component.

[tniezg]

Issue:
React is returning a warning about a missing key prop when rendering some Jest test results using the NoTests component (ie. tests could not be found).

What I did

Add a key prop to NoTests containing the value of the name of the test being rendered.

How to test

Add references to Jest test files inside withTests that are not yet present. For example, withTests('somenoneexistenttestsfilename').

Is this testable with jest or storyshots?
Jest
Does this need a new example in the kitchen sink apps?
No
Does this need an update to the documentation?
No
If your answer is yes to any of these, please make sure to include it in your PR.

[codecov]

Codecov Report

Merging #3111 into master will increase coverage by 0.23%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #3111      +/-   ##
==========================================
+ Coverage   35.84%   36.08%   +0.23%     
==========================================
  Files         432      438       +6     
  Lines        9407     9447      +40     
  Branches      884      879       -5     
==========================================
+ Hits         3372     3409      +37     
- Misses       5463     5489      +26     
+ Partials      572      549      -23

Impacted Files	Coverage Δ
addons/jest/src/components/Panel.js	0% <0%> (ø)	⬆️
app/polymer/src/server/utils.js	0% <0%> (-100%)	⬇️
addons/a11y/src/components/WrapStory.js	61.11% <0%> (ø)	⬆️
addons/a11y/src/components/Tabs.js	0% <0%> (ø)	⬆️
...ddons/actions/src/components/ActionLogger/style.js	0% <0%> (ø)	⬆️
addons/viewport/src/components/viewportInfo.js	36.36% <0%> (ø)	⬆️
lib/components/src/table/cell.js	65.21% <0%> (ø)	⬆️
lib/codemod/src/transforms/move-buildin-addons.js	46.87% <0%> (ø)	⬆️
addons/a11y/src/components/Report/Item.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/configs/handle_keyevents.js	33.33% <0%> (ø)	⬆️
... and 61 more

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