fs: http: fix isfile method

[sisp]

This seemingly minor change fixes pushing data to an HTTP remote storage with dvc v2.16.0. At the moment, dvc v2.16.0 cannot push any data at all to an HTTP remote storage!

I noticed that with dvc v2.15.0 pushing data to an HTTP remote storage works fine while it doesn't work - i.e. data just isn't transferred without an error - with v2.16.0. Between dvc v2.15.0 and v2.16.0, dvc-objects (a transitive dependency of dvc via dvc-data) was bumped from v0.1.5 to v0.1.6 by the bump of dvc-data from v0.1.5 to v0.1.6. After some digging, I arrived at dvc-objects and #114 which, among other changes, changed the implementation of the ObjectDB.exists(...) method:

 def exists(self, oid: str) -> bool:
-    return self.fs.exists(self.oid_to_path(oid))
+    return self.fs.isfile(self.oid_to_path(oid))

Now, FileSystem.exists(...) simply delegates the call to the underlying fsspec filesystem implementation, but HTTPFileSystem.isfile(...) overrides this delegation by a hardcoded return value True which makes the ObjectDB.exists(...) method always return True and prevents any data upload to an HTTP remote storage because every file is considered to exist already.

[codecov-commenter]

Codecov Report

Merging #116 (b314c2c) into main (ebee287) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #116      +/-   ##
==========================================
+ Coverage   67.10%   67.11%   +0.01%     
==========================================
  Files          39       39              
  Lines        2371     2369       -2     
  Branches      275      275              
==========================================
- Hits         1591     1590       -1     
+ Misses        750      749       -1     
  Partials       30       30              

Impacted Files	Coverage Δ
src/dvc_objects/fs/implementations/http.py	38.15% <ø> (-0.31%)	⬇️

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[skshetry]

Thank you @sisp 🙂