{bash,zsh}: align sessionVariables type

This matches `home.sessionVariables`.

modules/programs/bash.nix

@@ -137,8 +137,9 @@ in
           with types;
           lazyAttrsOf (oneOf [
             str
-            int
             path
+            int
+            float
           ]);
         example = {
           MAILCHECK = 30;

modules/programs/zsh/default.nix

@@ -247,7 +247,14 @@ in
 
         sessionVariables = mkOption {
           default = { };
-          type = types.attrs;
+          type =
+            with types;
+            lazyAttrsOf (oneOf [
+              str
+              path
+              int
+              float
+            ]);
           example = {
             MAILCHECK = 30;
           };