Pin version of nvim plugins lsp and treesitter

For using named plugins with neovim < 0.10 plugin versions not above a
certain value are needed.

.config/nvim/lua/plugins/lsp.lua

@@ -1,5 +1,5 @@
 return {
-    {'neovim/nvim-lspconfig'},
+    {'neovim/nvim-lspconfig', tag = 'v1.7.0'},  -- pin to a version thats compatible with nvim < 0.10
     {'hrsh7th/cmp-nvim-lsp'},
     {'hrsh7th/nvim-cmp'},
 }