fix not hardcoding "Project.toml" when fixing up extensions in manifest (#3851)

* fix not hardcoding "Project.toml" when fixing up extensions in manifest file

* abspath to be extra safe

---------

Co-authored-by: KristofferC <kristoffer.carlsson@juliacomputing.com>
Co-authored-by: Ian Butterworth <i.r.butterworth@gmail.com>
(cherry picked from commit 8875120)

Author: 3 people

src/Operations.jl

@@ -167,9 +167,11 @@ end
 # about extensions
 function fixup_ext!(env::EnvCache)
     for pkg in values(env.manifest)
-        v = joinpath(source_path(env.manifest_file, pkg), "Project.toml")
-        if isfile(v)
-            p = Types.read_project(v)
+        # isfile_casesenstive within locate_project_file used to error on Windows if given a
+        # relative path so abspath it to be extra safe https://github.com/JuliaLang/julia/pull/55220
+        project_file = Base.locate_project_file(abspath(source_path(env.manifest_file, pkg)))
+        if isfile(project_file)
+            p = Types.read_project(project_file)
             pkg.weakdeps = p.weakdeps
             pkg.exts = p.exts
             for (name, _) in p.weakdeps