Revert "Fix JLD2 julia compat"

[IanButterworth]

Reverts #93505

Pkg tests install MetaGraphs v0.6.4 (to test SemVer installation) which has an upper bound on JLD2 which was this PR made impossible to install on julia 1.9+

Unfortunately that means this change broke Pkg CI (which is tested on Base CI too)

add: resolve tiers: Error During Test at /home/runner/work/Pkg.jl/Pkg.jl/test/new.jl:906
  Got exception outside of a @test
  Unsatisfiable requirements detected for package JLD2 [033835bb]:
   JLD2 [033835bb] log:
   ├─possible versions are: 0.1.0 - 0.4.35 or uninstalled
   ├─restricted by julia compatibility requirements to versions: 0.4.28 - 0.4.35 or uninstalled
   └─restricted by compatibility requirements with MetaGraphs [626554b9] to versions: 0.1.0 - 0.1.14 — no versions left
     └─MetaGraphs [626554b9] log:
       ├─possible versions are: 0.5.0 - 0.7.2 or uninstalled
       └─restricted to versions 0.6.4 by an explicit requirement, leaving only versions: 0.6.4

(@v1.9) pkg> add [email protected]
   Resolving package versions...
ERROR: Unsatisfiable requirements detected for package JLD2 [033835bb]:
 JLD2 [033835bb] log:
 ├─possible versions are: 0.1.0-0.4.35 or uninstalled
 ├─restricted by julia compatibility requirements to versions: 0.4.28-0.4.35 or uninstalled
 └─restricted by compatibility requirements with MetaGraphs [626554b9] to versions: 0.1.0-0.1.14 — no versions left
   └─MetaGraphs [626554b9] log:
     ├─possible versions are: 0.5.0-0.7.2 or uninstalled
     └─restricted to versions 0.6.4 by an explicit requirement, leaving only versions: 0.6.4

[DilumAluthge]

For Pkg tests, if we want to make the tests more reproducible, we could checkout a specific commit of the General registry. That way, changes in the General registry won't cause the Pkg tests to fail.