Installing from a git branch is broken

[ngoldbaum]

If I specify a URL to install from with a branch specified with @, the correct branch is not installed.

When I make the following modification to numpy's asv config:

diff --git a/benchmarks/asv.conf.json b/benchmarks/asv.conf.json
index 7c7542b1ec..db5c89665a 100644
--- a/benchmarks/asv.conf.json
+++ b/benchmarks/asv.conf.json
@@ -46,7 +46,7 @@
     // list indicates to just test against the default (latest)
     // version.
     "matrix": {
-        "Cython": [],
+        "git+https://github.com/lysnikolaou/cython.git@nogil-build-flags": [],
         "build": [],
         "packaging": []
     },

Then instead of building that branch it builds the default branch.

I added some breakpoints to util.py and it looks like the regex logic in ParsedPipDeclaration doesn't account for this case and the branch is parsed as the package name.