Update Startup CSS files

This is due to
https://gitlab.com/gitlab-org/gitlab-ui/-/merge_requests/2756.

app/assets/stylesheets/startup/startup-dark.scss

@@ -452,9 +452,12 @@ a.gl-badge.badge-warning:active {
 .gl-form-input.form-control:disabled,
 .gl-form-input.form-control:not(.form-control-plaintext):not([type="color"]):read-only {
   background-color: #1f1f1f;
-  color: #868686;
   box-shadow: inset 0 0 0 1px #404040;
+}
+.gl-form-input:disabled,
+.gl-form-input.form-control:disabled {
   cursor: not-allowed;
+  color: #868686;
 }
 .gl-form-input::placeholder,
 .gl-form-input.form-control::placeholder {

app/assets/stylesheets/startup/startup-general.scss

@@ -438,9 +438,12 @@ a.gl-badge.badge-warning:active {
 .gl-form-input.form-control:disabled,
 .gl-form-input.form-control:not(.form-control-plaintext):not([type="color"]):read-only {
   background-color: #fafafa;
-  color: #868686;
   box-shadow: inset 0 0 0 1px #dbdbdb;
+}
+.gl-form-input:disabled,
+.gl-form-input.form-control:disabled {
   cursor: not-allowed;
+  color: #868686;
 }
 .gl-form-input::placeholder,
 .gl-form-input.form-control::placeholder {

app/assets/stylesheets/startup/startup-signin.scss

@@ -301,9 +301,12 @@ fieldset:disabled a.btn {
 .gl-form-input.form-control:disabled,
 .gl-form-input.form-control:not(.form-control-plaintext):not([type="color"]):read-only {
   background-color: #fafafa;
-  color: #868686;
   box-shadow: inset 0 0 0 1px #dbdbdb;
+}
+.gl-form-input:disabled,
+.gl-form-input.form-control:disabled {
   cursor: not-allowed;
+  color: #868686;
 }
 .gl-form-input::placeholder,
 .gl-form-input.form-control::placeholder {

ee/app/assets/stylesheets/startup/startup-dark.scss

@@ -452,9 +452,12 @@ a.gl-badge.badge-warning:active {
 .gl-form-input.form-control:disabled,
 .gl-form-input.form-control:not(.form-control-plaintext):not([type="color"]):read-only {
   background-color: #1f1f1f;
-  color: #868686;
   box-shadow: inset 0 0 0 1px #404040;
+}
+.gl-form-input:disabled,
+.gl-form-input.form-control:disabled {
   cursor: not-allowed;
+  color: #868686;
 }
 .gl-form-input::placeholder,
 .gl-form-input.form-control::placeholder {

ee/app/assets/stylesheets/startup/startup-general.scss

@@ -438,9 +438,12 @@ a.gl-badge.badge-warning:active {
 .gl-form-input.form-control:disabled,
 .gl-form-input.form-control:not(.form-control-plaintext):not([type="color"]):read-only {
   background-color: #fafafa;
-  color: #868686;
   box-shadow: inset 0 0 0 1px #dbdbdb;
+}
+.gl-form-input:disabled,
+.gl-form-input.form-control:disabled {
   cursor: not-allowed;
+  color: #868686;
 }
 .gl-form-input::placeholder,
 .gl-form-input.form-control::placeholder {

ee/app/assets/stylesheets/startup/startup-signin.scss

@@ -301,9 +301,12 @@ fieldset:disabled a.btn {
 .gl-form-input.form-control:disabled,
 .gl-form-input.form-control:not(.form-control-plaintext):not([type="color"]):read-only {
   background-color: #fafafa;
-  color: #868686;
   box-shadow: inset 0 0 0 1px #dbdbdb;
+}
+.gl-form-input:disabled,
+.gl-form-input.form-control:disabled {
   cursor: not-allowed;
+  color: #868686;
 }
 .gl-form-input::placeholder,
 .gl-form-input.form-control::placeholder {