Firestore: Add note about potential flakiness in the new Watch test

[schmidt-sebastian]

No description provided.

[codecov]

Codecov Report

Merging #5928 into master will increase coverage by 0.28%.
The diff coverage is n/a.

@@ Coverage Diff @@## master #5928 +/- ##
============================================
+ Coverage 46.51% 46.79% +0.28% 
Complexity 25648 25648 ============================================
Files 2456 2456 Lines 267490 267613 +123 Branches 29752 30563 +811 ============================================
+ Hits 124414 125241 +827 - Misses 133033 133113 +80 + Partials 10043 9259 -784

Impacted Files	Coverage Δ	Complexity Δ
...re/src/main/java/com/google/cloud/BaseService.java	55.55% <0%> (-6.95%)	2% <0%> (ø)
...le/cloud/compute/deprecated/DeprecationStatus.java	88.63% <0%> (-3.13%)	20% <0%> (ø)
...va/com/google/cloud/http/HttpTransportOptions.java	56.33% <0%> (-1.64%)	10% <0%> (ø)
...le/cloud/storage/contrib/nio/CloudStoragePath.java	75.67% <0%> (-0.69%)	51% <0%> (ø)
...ge/contrib/nio/CloudStorageFileSystemProvider.java	62.76% <0%> (-0.3%)	73% <0%> (ø)
...ain/java/com/google/cloud/logging/LoggingImpl.java	87.9% <0%> (-0.19%)	73% <0%> (ø)
...src/main/java/io/grafeas/v1/UpdateNoteRequest.java	11.74% <0%> (-0.08%)	11% <0%> (ø)
...in/java/io/grafeas/v1/UpdateOccurrenceRequest.java	11.71% <0%> (-0.08%)	11% <0%> (ø)
...ava/io/grafeas/v1/ListNoteOccurrencesResponse.java	14.28% <0%> (-0.05%)	10% <0%> (ø)
...in/java/io/grafeas/v1/ListOccurrencesResponse.java	14.28% <0%> (-0.05%)	10% <0%> (ø)
... and 168 more

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[BenWhitehead]

One small typo. Otherwise LGTM.