BlobGCManager deletes just written extent

### Which service(blob, file, queue, table) does this issue concern?
blob

### Which version of the Azurite was used?
latest

### Where do you get Azurite? (npm, DockerHub, NuGet, Visual Studio Code Extension)
GitHub

### What's the Node.js version?
14.15.4

### What problem was encountered?
BlobGCManager deletes just written extent.

I am attaching [fragment of Azurite log](https://github.com/Azure/Azurite/files/6055069/log.txt). You can see that just written extent 6b079744-d236-4978-bba6-4d2b669f95c1 is deleted by the GC.

### Steps to reproduce the issue?
Run test that perform multiple GET/PUT/DELETE requests. After about 1 hour of testing GET for one of previously written objects permanently fails with HTTP error 500.

### Have you found a mitigation/solution?
No